An overly full fridge can lead to warm spots and the fridge door can act in the same way. You want to avoid keeping things on the door that can spoil quickly, mainly dairy. The door is constantly opened and closed exposing it to the warm air of the room. If you're like me standing there like a zombie staring blindly for something to eat at 2 a.m those items on the door have spent too much time in the warm air. Over the course of the day, this surprisingly adds up.