In terms of physics why would you bake a potato in aluminum foil?

I guess the foil traps heat and cooks it faster by reflecting heat radiation back inward toward the potato. But the outside is reflective too so now I dont know witch way the heat is going.

You usually wrap a potato in foil when cooking on the grill, and my guess would be to distribute heat all around the spud for even cooking. Instead of having all the heat directed at the bottom of the potato.