When I bring my car home from the cruise ins I pop the hood to let the heat out. The engine will actually get hotter sitting there and will turn on the electric fan automatically. I have a switch for the fan if I decide that I don't want it running but I just leave it on. I never does drain the battery down. It will come on one time then shut off and then come another time then it doesn't come on any longer. It more than likely doesn't make a difference but getting the heat out of the engine bay might make stuff like hoses, wire, etc... last longer. A hood closed with no air circulating is as close to a oven you can get. lol
Good question.