Perhaps one of the first important things children learn is that the Earth is round. It's an important illustration to children of the ways that reality can be different than it seems at first glance. This fact is poorly conveyed with a regular flat map. Globes are a beautiful and useful tool to convey some of the wonder of the world as it has been revealed to us by science.
Globes as Decoration
Globes have advantages as decoration. They come in wide varieties. There are classic desk globes, gemstone globes, extra-large floor globes, and even magnetic globes that seem to float in the air. The advantage in all these is the simple wonder of displaying our round Earth as it actually is.
The globe is a physical object that can be touched and felt in a way that a flat map can never compete with. It has been shown in experiments that certain people learn best when they can experience facts physically. A visual aid, such as a flat map, is not enough for those who relate to ideas through their feel and touch. Much more than a flat map, a globe is a physical object that can be manipulated and handled in order to understand the Earth. Children and adults who learn kinesthetically, by doing things, will find globes easier to understand.
Contrary to myth, the Western world did not discover that the Earth was round after Columbus's trip to America. This was a well known fact of educated people since the ancient Greeks. Globes have existed as long as maps have, and it has always been an advantage to different peoples in different times to be reminded that the reality we live in is different than it immediately seems.