During summer, it freezes water at night when it's colder outdoors, to let the ice melt during the day when it's hotter outdoors.  

During winter it lets cold outdoor air into the refrigerator/freezer to save electricity. 

During spring and autumn it saves electricity too because outdoor is usually (especially at night) colder than indoor.  It also can freeze water at night to let it melt during the day to save even more electricity.