Light Fixture Insulation ?

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 don’t have the yellow in the back.

I get different stories on what the yellow is for. Some say it’s to keep the bulb heat from cooking the wires and wire nuts in the box. Others say it’s for keeping out drafts and air leaks around the box.

Any thoughts on what it’s for and have you ever not used it?