In 2011-2012, the use of social media rose rapidly with a marketing impact across the web. Social sharing became the norm and the search engines were starting to notice! Google in particular began to look at the social signals that were being utilised and soon brought this into its results.
A complex algorithm had to analyse and personalise results to each and every individual based on their logged-in profile looking at content shared by the searcher's social circle. The results may not appear up on the top 10 in the search engines results, but they are undoubtedly promoted within the rankings because of the social influence.
So why is social power so useful to any business? Well let's take a look at social circles, one tweet, one like may show to a socialite that has say 100 followers or friends. If only 10 of those friends then share or promote your information, then you reach a potential target audience of say 1,000 (if all followers / friends have 100 followers or friends!). So it's not rocket science... for any publisher, and by that I mean you or I, it is beneficial to have your content shared. For Google searches this is especially true of content shared on Google+.
Once more it's free, you are essentially asking a few people to spread the word, in essence doing some of your work for you!