The coils behind the fridge can get dusty, which eventually can result in the fridge needing to work harder and not being as energy efficient as possible. Similar to how an HVAC unit works harder and uses more electricity if you don't change the air filters on a regular basis. Once a year, you should pull the fridge away from the wall and clean the coils in the back with either a duster, a soft bristled brush, and/or a vacuum. Make sure you do this with the power to the fridge turned off to be safe.