In the summer, when you drive somewhere, go inside, come back to your car and find its still comfertably cool from the AC on the journey there. Also works vice-versa on heat in the winter.
*Jim walks back to his car after buying soup in the hot summer*
"Gosh, my car is still nice and cool! Its the leftover AC! Yippee!"
*Shannon gets into her car after buying soup in the freezing winter*
"My car is still toasty warm! Leftover heat!"