Quote Originally Posted by Mega Dux Bob
Castle defense; the walls need a unit to man the towers so just throw the expendable peasants out to man the outer walls to bleed the enemy and keep your high value units in the inner defenses.
I would say that this one is about the best.

They are cheasp to get and cheap to have as upkeep. They should also kill a fair number of troops on the walls themselves. So 5-6 units of Peasants on the outer walls would deplete the enemy enough for your inner walls to take care of the remaining enemy.
Of course better troops might do better, but we generally don't like to sacrifice them, and as such sometimes were end up being too reluctant to put them in certain harms way, until it is too late.
Also the Peasants will be able to sit in castles while you shift the real troops around, defending and attacking.