depends on the army, really.
if It's my brand new, proper round circle army like my deep kin, I'm trying to fully paint my army and not have a grey model. (got one unfinsihed base though... I just need to buy water effects or something for it. ) just because I like painting my eels and sea elves. I have a story in mind, and I'm doing it!
for my square based, mostly second hand death army? yea.. I play with half of it unpainted and not on proper bases. mostly because I ran out of calvary bases and circle bases for it. I really should finish them, but I'm just not in the mood currently to paint all those skeletons.