Avatars have several uses in the world of education. What student wouldn't want a self-created image of superstar quality for his or her profile photo? They are definitely an engagement tool. If your students are young or safety and security is a concern, avatars conceal one's real appearance. Sometimes we just don't want a real photo floating around in cyberspace and an Avatar is a great way to avoid that.
Even for me, a technology teacher with a fairly strong online presence, I don't necessarily want personal images popping up when someone searches for me.