Freezer Best Cooling Performance
The less empty space there is in the freezer, the better it will cool. This is because the items in the freezer absorb the cold and help the freezer maintain a steady temperature, in much the same way that ice cubes keep a drink cold.
When you open the freezer door, the cool air rushes out and warm air rushes in. The more cold items in the freezer, the less cool air is needed to keep the freezer cold. Therefore, when you close the door again, the freezer returns to a stable temperature more quickly.