Board Thread:Questions and Answers/@comment-1490123-20140723223236/@comment-14600979-20140723224256

I think the "player and enemy" was just an example use.

You use it for... mass designation of sprites. Say, you have dozens of bullet sprites, you don't want to have to track collision for each one. This makes it just "is one of the entities in this group in contact with one of the entities in this group".