Other than pan frying something like chicken, I don't really have "leftover fat".

Bacon - ya pour that right into the bacon fat container that has its own strainer.

Most other recipes the fat is part of the dish. As someone else commented - fat is flavor. Say you brown chicken parts for something like Gumbo, the next thing in the pan will be vegetables that get glazed, and you're gonna need a fat for that which is already there in the pan.