It will catch the dripping fat and make for easier cleanup, it will provide some moisture in the cooking chamber, and it will serve as a mass of heat to help keep the temps even.
If your pan needs extra loving, you can re-season it by scrubbing it clean and applying a film of fat all over the pan's interior and exterior, then placing it in a 500 ˚ oven with a sheet pan or foil underneath to catchdrips.