I would say it's fairly minor, but the non-unique units I sometimes like to build well past their heyday are: Pikemen, Airships, Scouts and Galleons.
- Pikemen may obsolete at rifling, but they don't truly obsolete from the battlefield until the AI gets gunships and their cavalry disappear. It's common for the AI to have leftover stacks of cavalry roaming around an otherwise infantry+ battlefield. Obviously, the main benefit of pikemen as opposed to riflemen is that you can build them and dedicate hammers to your war effort before you get Rifling. In the battlefield I find they have several small uses. If there's a lone horse or another very weak unit, it's generally a pikeman I use to mop that up. They're super vulnerable to counter attack, but that's exactly the point, I'm good with trading a 60
unit to knock out an AI's 120
unit. I wouldn't want to lose a rifleman or something in this manner, and I generally don't want to slow down the entire stack or weaken the attacking push to provide adequate defenders just to mop up one unit. Pikemen can also make ideal city defenders in some modern situations, where the city is likely safe from enemy attack and is at most potentially vulnerable to an errant horse running its way. It's also common after a big stack battle against a city to have a couple super weak leftover defending units after your first attacker withdrew/failed. A 60
pike is as good at cleaning up an injured 3 str unit as an infantry is. And of course they're good as late game happy police after you've added some more AI cities to your own and cheaper units are unbuildable.
- Scouts: These aren't meaningfully improved when upgraded to "explorers" as their main benefit is just being a 2-mover, so I may build one of these to scout the AIs / as a super medic.
- Airships: I am not a fan of an air force (results in even exchanges with the AI), but the scouting from these guys is without parallel. So even if the enemy is going to have fighters I may want 1-2 airships just to scout. The slight dmg they do is also enough to tip the scales of a 50/50 fight assuming it's away from intercept units.
- Galleons: I'm not a fan of navies (results in even exchanges with the AI). My navy is primarily just to transport units over. The strength of a transport compared to a galleon is basically irrelevant - both will get mopped up by an enemy destroyer. Not only can galleons be prepared long before transports, but at 80
for 3 cargo compared to 125
for 4 cargo they compare favorably to transports at a 26.7
/cargo cost vs a 31.25
/cargo. Transports have 5 movement speed compared to 4 with galleons, which may or may not matter at all, and makes even less of a difference with circumnavigation/refrigeration.
then it can actually be a disadvantage to unlock bigger units early.
