Google Play Games is both an app and a game service. In many games, before you start playing, you’re prompted to log in to your Google account. Then you will be able to get achievements, leaderboards, and possibly even the game’s save state synced across all of your devices. This process can be cumbersome on a phone, less so on a TV, because you may need to pick one of several Google accounts synced on the device. If you haven’t opted into Google+ yet, you’d have to do so beforehand.
Google has been decoupling Google+ from many of its apps recently, including Hangouts and Photos. This will now be applied to Play Games in an upcoming update to Google Play Services.
One new feature is automatic sign in. You can apply a single account to be your main gaming account and you won’t need to authenticate when starting a new game. The process will be seamless, giving you instant access to your achievements on any device.
This may be a privacy issue if any app could access your Google+ account information, and so Google has taken out the Google+ requirement. New users will be given a unique id, but it won’t be usable to identify their Google account.
Games that do actually use your profile can continue to request the Google+ API, but decoupling the two means that more gamers can start using this service without using Google+ and more game studios may consider using Google Play Games to add more features for users. However, users that have already signed up for Google+ will continue to have their player id coupled to their Google+ profile. The announcement was unclear if that’ll be true for all games and not just ones you’ve already begun playing.
The change should be coming in the next few months, perhaps by Google I/O. There was not any official timeline for this change, but it is something that both gamers and developers should be aware of.