Much like the other forms of traffic data, social media traffic data in Google Analytics contains important information about sources, such as Twitter and Facebook, engagement, goal influence and user behavior.
There is even social plugin (Facebook Like, Google +1, Twitter Retweet, etc.) engagement data (a great resource if you're testing optimal share locations). As link-building continues transforming into relationship building, monitoring social traffic sources may become as common in your SEO campaign as keyword research.
This addition to Google Analytics as well as the recent algorithm changes reinforces our stance that traffic and conversions, not rank, should be the measure of a successful campaign.