That's a very good question, and I'm sure that many smart people at Google asked the same question before they launched Google+.
Google+ offers a bevy of features that allow you to share different things with different people.
Google+ makes it downright simple to share particular things with only certain people.
Facebook is invested in your sharing things with the widest audience possible, as the default privacy settings reflect. Lately, Facebook has gotten better about allowing you to choose who can see what, but Google+ was designed with choice in mind.
Circles, Photos, and Hangouts
by Scott McNulty
Peachpit Press, 201
Book Stall Review: The Google+ Guide
Artwork: Réseaux Sociaux