Everything Google is doing, from Google+ to semantic search serves its mission “to organize the world’s information and make it universally accessible and useful.”
In order for Google to provide the most relevant search results, it looks beyond the keywords to find context of your query based on your connections and social signals, +1’s, shares, likes etc..
Google Authorship ties you to your content no matter where you publish on the web where “rel=authorship” is installed.