interesting you named two foods i would not put cheese into, shepherd's pie & chicken pot pie.
I like to put the cheese on the top of the shpherd's pie, although i know a lot of recipes do not call for it.
on top of the mashed potatoes?
I've seen - and tasted - lots of Shepherd's Pies that have had shredded cheese baked onto/into the mashed potatoes. Good for color, texture and taste. YUM!