It’s a way to filter content.
Think about it, Google supplies content. But there is so much content out there so that it becomes useless, because you don’t know how to pick what to focus on.
Online we are since the beginning of Facebook used to let our friends decide what we will become exposed to. This is something that Google + can help you with.
How will they get more people to sign up for Google + so that they can own a little bit more of the world and earn a little bit more money?
Through games they also provide people with the opportunity to play games and meet new people through the games. The games makes people use Google + more.
Just competition between Facebook and Google or what do you think?