Hello,
Interesting question. I would say that the number one benefit is the way that it is able to connect niche groups of people. The huge online audience allows people with similar ideas and backgrounds to come together more easily than ever before. In the past, we were more limited to networking with people near us, and now we have the whole world at our finger-tips.
This allows for things like public activism and the democratization of information, which aren't necessary new but have just be well aided by social media.