Social Plugin Tracking generates three reports: Social Engagement, Social Actions and Social Pages. Social Engagement tracks behavior changes (time on site, pageviews, bounce rate, etc.) for visits from social plugins. Social Actions tracks the number of social actions users take on your site, and Social Pages compares your pages on the number of social actions they are receiving.
These tools give website owners a great deal more insight into the impact of social on their websites. Tracking social just makes sense, especially as social sites drive more of the web’s traffic. We also suspect that Google also wants to encourage more sites to adopt the +1 Button. Raw data showing that +1s increase web traffic is the most convincing thing Google can provide.