Dirt is a good insulator for ants and worms. Some people put snow against their house because it keeps it warmer. Carpet is an insulator because it keeps the cold out. The thicker it is the warmer it is. Leaves can be insulators for animals to keep them warm.
Leaves can keep seeds from dying.
Foam is an insulator that you can also sit on. Leaves keep new sprouts from freezing in the spring. Also leaves keep rose bushes from freezing. Fiberglass keeps the heat from getting out of your house, and it saves electricity. Dirt keeps the roots from freezing.