The new usernames are tied to your email account and you can decide whether to keep your activity public or private. When you need to search for friends, you can do so with their email -- something developers can make easier now that access to Contacts is also decoupled from Google+. There's also a new sign-in process that only requires to you enter your credentials once per account rather than once per game. If you haven't tried Google Play Games yet, you'll be prompted to pick a Gamer ID when you log in for the first time. Existing users will be prompted to do so when signing into a new Play-integrated title. The company began nixing the Google+ requirement last year, starting with YouTube before moving on to other apps and services.