VMXA said:
"Sometimes it might make sense to block it, but in general not so much. " Why would it make sense to not block a settler heading for a hole in your empire? I could understand not being able to block it, but no way would I let them found a town in my land, if I could prevent it.
As The_Professor points out, it takes units to block settlers. In the ancient age I usually have warriors or scouts to get contacts, workers to develop land, and settlers to found cities. I don't want to mess up my worker development in general for blocking, as I want my cities to develop well. I want contacts ASAP, so the warriors need to go exploring. More warriors to block units would mean later builds on markets, libraries, great wonders, or barracks whatever sort of infrastructure I want to get up/pre-build for (temples pre-build libraries for example). So, how would blocking settlers really come as worth it when it delays my civilization's development in general? And where would I block AI settlers?
The first ring of cities will produce well, and there exists no need to block AI settlers there. That's already 7 to 9 cities, which will give me most of the commerce and probably production for most of the game (notice how 5 CC games compare to regular games). The second ring sort-of works out productive, but given 6 to 8 cities in the first ring, I'd estimate there's *at least* another 8 spots for cities in the second ring. That's plenty of spots to grab without blocking.
19 settlers or so from your capital keeps it as a settler factory perhaps for too long. 15 cities on a standard Deity map comes as a fair number (before any wars, if that happens) for an agricultural tribe with a cow and 4 BGs in the capital. And to grab all of those spots via blocking requires extra units, which slows down your cities development (even if you want to go barracks-horseman/swords). Second-ring cities also often require extra time to develop. So, I don't see AI settler blocking paying off. I can't see blocking for 3rd ring cities paying off, since it takes quite a while to develop those cities into something useful. May as well let the AIs settle, grow and build things for you, and then capture them.
That's for upper levels. For lower levels, the AIs produce settlers slower, so there exists fewer settlers to block. And often enough you can settle CxC from the AI, put in a library or temple and get the border squares fairly easily. So, I don't how settler blocking with units pays off in general, though of course play as you like. Settling near or on a luxury ASAP comes as another story.
EMan perhaps put things best.