Some new ceiling light fixtures come with yellow insulation stuffed in the back. And then on the bulb side have a reflective insulated thin sheet. Some dont have the yellow in the back. I get different stories on what the yellow is for. Some say its to keep the bulb heat from cooking the wires and wire nuts in the box. Others say its for keeping out drafts and air leaks around the box. Any thoughts on what its for and have you ever not used it?