When is it necessary to put foil over a pie's crust? In the past, when I have made pumpkin pie, I have never put foil around the edge of the crust of the pie.  Yesterday, I baked a pie with someone else, and they insisted that the foil was necessary to prevent the pie crust from burning.  I have noticed the a lot of recipes for pies other than pumpkin (frequently covered pies like strawberry-rhubarb) explicitly call for aluminum foil on the crust.

When does a pie crust need to be covered in foil while baking?
Generally speaking, when the length of the cooking time required to cook the filling correctly is such that the crust would burn if it wasn't covered. 

It is usually more necessary when you have blind-baked the crust, but I must say I've cooked a lot of pies in my time and never covered the crust because I'm always careful to par-bake the crust just enough to seal it and no more.