sometimes you have a hand that has significant value, but can't stand a raise from your opponent – i.e something like KT on a K high dry board or something – in this case, if you bet, you can get check raised by both set type hands and air hands as well, and its really hard to play. but if you check behind, it means that the pot is smaller so you can now call any turn and re-evaluate to see whether villain has a monster, or whether this is air. so you minimise your risk against the strong hands, and pick up value against bluffs. 

i hope that makes sense, please tell me if i am wrong.