With groups, you can challenge your friends and keep track of them within your own group, rather than have them mixed in with everyone else.
You can also personalize your group to show scores and news articles from your favorite teams, along with uploading your own logo. In the long run, you'll be able to set up a url and basically host your own bracket. That part won't be done for this season, but hopefully for the 2015 bracket.
Don't have a group yet? Start one! It's quick and easy, just fill out a form and invite your friends!