They give more cluster space by providing a lobby which helps relieve congestion. They help cool the hive in the summer, regulate air flow in winter and shield the front of the hive from old man winters icy draft, which will allow the queen to lay eggs closer to the front. They will keep pesky racoons form reaching up into the cluster and grabbing a paw full of comb. They are relativity cheap to build. This is a simple and time proven piece of equipment that has a thumbs up in my book. I use it on all of my hives.
The Busy Bee teaches two lessons: One is not to be idle and the other is not to get stung.