Easy sign up and sign in
The Google+ Sign-In button is an easy way for users to sign up and sign in to your app. This allows you to know who they are on Google+ and to build a more personalized experience for your app, all without having to create yet another username and password.
Be shared and discovered
The Share dialog provides a means for users to share rich content from your app into the Google+ stream, including links, photos and location. When users log into Google+, the stream is the first thing they see, making it core to the Google+ experience and giving your content greater visibility.
Increase app discovery and drive lasting re-engagement
Want to increase the visibility of your app? With a user’s permission, you can display activities they take on your app on their Google+ profile, visible to people they choose to share with. These relevant mentions of your app can foster conversations, and create powerful social proof for your service.