What is the "proper" use of Peasants?

[homem_de_ovo]

To try and make clear exactly what I'm asking, for most units, they may have certain special powers, but it's clear what their base function is. Soldiers fight, Explorers complete landmark expeditions, etc. As I understand it, Peasants are supposed to build the Farm improvement on Vassals or Outpost goods tiles. But this situation comes up so rarely that there might as well be an Achievement for it and I have a hard time believing this is the *base* use of the Peasant. Is there something I'm missing here?

The only reason I can imagine somebody *wanting* Peasants explcitily is if they planned ahead and took the Spartans National Spirit beforehand. This allows you to let the Peasants rack up the XP they need for Knight promotion on their own without having to waste your time roaming the map with them looking for Barbarians to kill. Given that Peasants are one of the few (or only, even) spawned units that appear per Vassal you can rack up a nice free army pretty quickly- with the added bonus that I think the Knight unit is at least in an upgrade line that goes through Gunpowder. Which is actually another nitpick of mine, that the Spartans/Raiders/Samurai can't be handed a gun when the later Ages come around. Someone will argue that since they were "free" units it makes sense that their window of usefulness has a limit to it, but given that this hack with the Peasants already exists in the game I'm not sure what the harm is letting you upgrade the other unique units. All in all the Peasants really feel like a unit that "should" be in the game because they're historical but what to do with them really wasn't thought out that well. They would probably work better being harder to get and working as a Prospector unit to spawn agriculture-based Goods tiles where desired.

[archonsod]

You can't use build farm in a vassal or outpost territory, only in your capitals. I wouldn't underestimate that aspect of them though, since you spawn two per vassal that's coincidentally exactly the amount you need to run a mill if there's no grain or rice resource present. Comes in handy if you're about to go on an integrating spree - call banners, integrate a bunch of vassals and you can use the peasants to slap down farms without having to worry about running out of IP (and if you do have plenty of IP, you gain the ability to go straight to mill / oven which gets those newly integrated cities growing nicely). Makes up for losing the 50% growth boost for no longer being a vassal.
Military wise they're basically militia. Slightly better than city guard, though not by much. They're good at defending towns, capitals and castles, with vassals being the obvious beneficiaries there. If you get them early enough they're also reasonable meat shields for crossbowmen; they're unlikely to do much themselves unless the enemy are still fielding spears, but they can take a few hits while your ranged units delete the enemy, and since they're free it's no big loss when they get taken out. Can be quite handy up through the gunpowder era if you end up at war; peasants give you an instant garrison, the freespawn helps keep them alive when attacked and if they survive enough attacks you convert them to knights to shift over to the offensive.