Your freezer works better when it's full. That's because the frozen items help keep the other items cold as well as help maintain the cooler temperature in your freezer.
If your freezer currently has some extra space – don't worry – we're not telling you to buy more groceries to fill it! All you have to do is throw in any extra ice packs you might have or fill up some plastic to-go containers, plastic baggies and/or empty milk jugs with water and add them to the freezer. (Leave some space when filling them, however, since water expands when it freezes.) It may seem silly, but it'll help your freezer run more efficiently and save you money on your electric bill.