I think it's obviously great for marketing and networking, but I also think it's contributing to a bit of a societal decline.
People have become more image-obsessed than ever before. Someone made a point in another thread about women starting to look the same: same eyebrows, same lips, same style of hair and clothes, same poses. And I agree.
Also, I think it encourages people to neglect their real lives and turn to the sleek, polished life they've cultivated for themselves on the web.
Last week I was late to someone's birthday party because I was taking selfies in my bedroom.
The lighting was so good I couldn't resist.

Like...that's sad.
But...overall, I think it's helped open up a ton of careers for people, and it definitely helps if you're an artist trying to promote your work. So I like it.