Edit - Peasant armies as anti-rebel patrols?
well i said i use them for that just in case they are extra outnumbered, for example they have one or two units and i have full stack of peasants.
check this picture

i had a full stack of peasant army near dumatha, and every bloody turn rebels pop up, so i cicled few plebs units to kick them and other to keep order i dumatha. and this 4 gained extra xp, others were not that lucky.