In RTW I train peasant units usually for either of two reasons: 1. To increase the garrison and prevent the town from rioting, which is quite a temporary "patch" to the problem at best--look for a more permanent cure to prevent riots; or 2. To reduce the population of a town and transfer them to another town that needs more people to grow, by disbanding the peasants in the latter place. You couldn't transfer people any other way, in my belief. And I have no compunction about disbanding any cheap units that I built--especially if they have no chevrons or weapon/armor upgrades. But be careful with the second one! I recently had a campaign (in XGM) where I built about twelve units of peasants in (too-overpopulated to the brink of rioting) Ariminium, marched eight of them across North Italy, loaded them in a Bireme, and brought them to Masilia, which I recently wrested from the Spanish and the town was very underpopulated. I disbanded 1, 2, 3, 4 units of peasants, and public happiness slowly grew nicer (I monitored it each time I disbanded a unit). My mistake was when I disbanded the 5th and 6th unit without monitoring, and before I got to the 7th, the public was in the red and about to riot! Maybe because I've reached more than the limit for a small town or because of cultural differences (or both), but I tell you this as a warning. Sometimes you could overdo it. Hawooh.