The problem with switching to communism in stock game is that if you've played republic/monarchy to its max potential you've farmed the heck out of your non core cities. And that means having a buncha ICS farm cities that are ill suited to becoming communist core cities with courthouses, police stations, factories and powerplants. So when you switch into communism, you need a while to develop them. Most people are already on their path towards winning by that stage of the game. Switching would just slow their finish time down. But yes, if the game is still competitive and you wish to fight non stop to win, communism is worth it.
Getting max potential out of Rep/Mon most certainly doesn't instantly mean using a ICS strategy. Assuming a high tech rate or going out of your way to obtain them, even if you would play very aggressively on high difficulties, you wouldn't reach OCN before the very late Ancient Era/early Middle Age. Specialists towns/cities only start becoming useful from that point forward earliest.
Even on Sid difficulty without using exploits, you can already win domination/conquest victories on smaller sized maps, or are about to by this point of the game. Given how many bad and unnecessary techs the Medieval Era has, many players wanting to win this way would and should end teching after obtaining Chivalry. The Celts don't even need Chivalry at all, and the Iroquois may not as well. This would therefore make ICS completely redundant. Making all those settlers to produce scientist or tax collector cities would only severely hamper your ability to close out these types of games quickly. Even under domination you would simply be better off either taking their cities, or razing and building cities in a CxxC or CxxxC formation, rather than a CxC formation.
Instead, let's say you want to win by a different victory, or want to win domination/conquest on larger sized maps. Then it's neccessary to go to the Industrial Era and beyond, and thus specialist farms do become essential. However, even then ICS isn't more often the best strategy to take. Usually under Republic, you already want to obtain or trade for at least 6 luxuries. With marketplaces in your core cities, and assuming Emperor+ difficulty, no WW or war happiness, GWs, entertainment buildings, entertainers or 10%+ luxury slider, you can now have 6 happy, 1 content and 5 unhappy laborers in them. Also, throughout the Middle Age it's usually best to build some workers or settlers in your non-core cities first to irrigate/road the surrounding territory, thereby reducing the population and not yet making full use of the specialists. This is relevant when we will now take a closer look at ICS.
Most importantly first is that compared to agricultural trait civs, ICS isn't even more efficient than using a wider city placement. Let me demonstrate using some math under Republic:
- ICS: 1 town per 7 tiles, rather than 1 city every 13 tiles. So needs about x1.86 the amount of settler factory cities compared to a wider city placement. However, this amount of efficiency you will never achieve, so a 1:2 ratio is more realistic. So that's twice the amount of settlers and granaries. However, granaries cost little maintenance, and won't pop out infinite amount of settlers. So a 1/6 division of its production cost is fair = 10 shields. A settler is needed for every town (duh), so that's 30 shields, plus 20 food if you have a granary, which you should have. 20 food is about equal to another 20 shields (forced labor is about a 1:1 ratio). Every town will also have +1 unit support.
Given 91 tiles, that's 13 towns, equaling
13 unit support. In total that's 60 shields per town. Given 91 tiles, that's 13x60=780. That's a
8.57 per tile shield cost. Even though you likely have +6 uncorrupted shield production under ICS compared to a wider spread (due to 90% corruption of all remaining shields), you will also likely lose out on a few food since railroaded irrigated tiles generally give 3-5 food (only not for tundra/hills/mountains or non-agri deserts, which are rather sparse), compared to the standard 3 of city center tiles. So this cancels each other out. The amount of beakers will be in between 1 (assuming higher science expenditure) + 6-9 beakers (depending on tile underneath) = 7-10 beakers total per town. Times 13 we get
91 to 130 total beakers.
- Wider spread: 1 city per 13 tiles, rather than 1 town every 7 tiles. Now you need half the amount of settler factory cities, but you will need an aquaduct (as long as not placed along a river/lake/sea). But lets assume there aren't any rivers/lakes/seas, so every non-core city needs an aquaduct. You don't need Temples since a general CxxC or CxxxC spread will already bring you to 12-13 tiles. But just to be 100% sure for particular CxxxCs, let's throw in one temple for every 6 cities. There's no need for marketplaces since even without them, no war happiness/WW, military police, no entertainers, no city improvs/GWs and 0% luxury/entertainment slider, you should already have 6 luxuries for your core cities as mentioned earlier. This is enough happiness to be making use of 7 laborers per city. As mentioned, you're better off producing some workers/settlers first, so by the time you hit size 12 in these cities, you will already have teched Steam Power. Assuming size 12, you need at least 5-8 laborers (depending on the type of tiles underneath) to make full use of the specialists. Only for nearly complete desert/plain tiles (desert under agri traits), which already would be rare to have, you need one extra happiness, which you could and should already have through some war happiness, a GW, or even a single Temple. So that's 50-100 (depending you're agricultural or not) + 5-10 for Temple (whether you're religious) + half the amount of settler factory cities compared to ICS (=30), which equals 85-90 for agricultural + relig/non-relig per city, and 135-140 for non-agricultural + relig/non-relig per city. Every city has +3 unit support.
Given 91 tiles, that's 7 cities, equaling
21 unit support. And given 91 tiles, that's 7x85 to 90=595 to 630 for agricultural civs, and 945 to 980 for non-agri civs. That's a
6.54 to 6.9 per tile shield cost for agricultural civs, and a
10.4 to 10.77 per tile shield cost for non-agri civs. The amount of beakers will be in between 1 (assuming higher science expenditure) + 12-18 beakers (depending on tile underneath) = 13-19 beakers total per town. Times 7 we get
91 to 133 total beakers, which is just slightly more, but lets just say its pretty much the same.
So ICS is about
25% to 30% more expensive than a wider spread for agricultural civs for the same amount of beakers/gold/shields, and about
20% cheaper for non-agricultural civs. And a wider spread even has a small benefit of having a bit more unit support.
Beyond that, ICS also has other significant certain drawbacks which can't be overlooked:
1) First, even on Sid difficulty without using exploits, you can obtain a tech lead by the mid-Industrial Era, no matter what map size you're playing on, or city spread you're using. This would make the largest benefit of ICS redundant.
2) Second, ICS is antagonistic to Communism later in the game. You would now need twice the amount of factories, power plants and offshore platforms (and if you're playing on very large maps with conquest/domination in mind, even manufacturing plants as well). This also not only requires twice the amount of shields, but also twice the amount of maintenance. And as shown in my previous comment, Communism is absolutely worth the switch, where each turn in Anarchy is earned back by 3 turns in Communism. Even if you're playing as a non-agricultural civ, the initial 20% increased earlier shield cost is earned back in a rather short while. It's about 10 more shield cost per build city per used tile, so assuming a fair 50-turn period, that would amount to 500 shields difference per town/city. Where under ICS Rep towns would be producing a mere 1 shield per turn, this would be about 20-25+ uncorrupted shields (checked this in my game) under Communism for those former Rep towns. And these 20-25 uncorrupted shields can still be raised even higher with a nuclear plant and a manufacturing plant. So that's a return investment within 500 / 20 to 25 = 20 to 25 turns for non-agricultural civs, which would be even lower with additional buildings as mentioned. For agricultural civs a non-ICS city placement will already be beneficial.
3) Third, I completely forgot to mention activating wartime/mobilization in my former reply (I could mention a Golden Era as Germany/America as well to buff Communism even further, but that is rather rare, so I won't mention it as a seperate point). As if Communism isn't already powerful enough, every single of your cities that's done building aquaducts, factories, power plants and offshore platforms (and perhaps a few marketplaces, harbors, granaries, hospitals, courthouses and police stations here and there), can now start producing a ridiculous amount of extra shields on top of what it already produces. ICS towns can never do that, and never to the same potential as wider spread cities can under Communism. If every city would be producing a unit or building mobilization has an effect on, that would net me about another 1000-1200 uncorrupted shields. Under ICS Rep this would only be about 200 uncorrupted shields, tops.
4) Fourth, as mentioned earlier ICS is also antagonistic to winning conquest/domination games early, even on Sid difficulty. This can usually only be done on tiny and small maps, and particular smaller standard maps.
5) Fifth, rather self-explanatory, but ICS should never be used for your core or semi-core cities as long as you haven't even yet reached the OCN. Not only through corruption, but also by giving you control over less territory in the beginning expansion phase of the game, thereby limiting yourself essential strategic and luxury resources.
6) Sixth, even over the OCN as Communism, corruption and waste ranks up
very slowly. In my 40% Standard game, where OCN was 108 and I was at 117 cities, every 10 new towns/cities would only gain me about 1% for both corruption and WLTKD-discounted waste. That means that every new city will still be around 35% corruption, and 23% waste with a marketplace.
7) Seventh, given point 6, ICS may actually however be beneficial for tundra/mountainous/deserts as non-agri under Communism. On one hand the benefits aren't that great to begin with, and these tiles usually only serve as taking up territory to prevent other civs from taking them, but long-term it may still lead to a small benefit regardless. Do note that towns on tundra/mountain closer to your capital shouldn't be used as ICS, since it would only end up ranking up corruption for your core or semi-core cities.
So when might ICS actually be more useful? Perhaps if you're a non-agri civ that is able to close the game somewhere in the Industrial Era, or the early Modern Era, where the benefits of a non-ICS Communism can't be benefitted from yet. On higher difficulties only Diplomacy victory comes to mind, or very particular domination/conquest victories that fit just within the right timeframe (like mid-sized maps). That is off course, once again, assuming not using severe exploits like the Great Library elevator, trade route pillaging, or ridiculous amounts of armies the AI all can't use themselves.