Excerpt from this article:
The fav began its public transformation from a garden variety feature into one of the most complex and cryptic forms of online communication. We started naming our favs. The ‘hate fav’ was born. So was the ‘flirt fav.’ And twitter responded, making favorite counts public on its new user profile pages. We saw that some had faved tens of thousands of times! The fav had taken on a life of its own. It was time for science to intervene and tell us why we fav.