There are plenty of arguments to make in favor of synchronous, face-to-face etc communication, about the loss of privacy when you broadcast everything you do, about the lack of personal engagement in this kind of communication, and so on. I can see making a judgement call whether to participate in this kind of communication, because there are plenty of drawbacks and negatives.
However, it's obvious to me why people are willingly switching some(most?) of their communication to it. Just as we learned to use asynchronous I/O in place of synchronous, we started using multicast messages and event-driven notifications instead of polling over all your friend-handles "hey what did you do today". It seems like a natural progression to me.
In terms of "social" I see it as a mostly-write type environment - I don't sweat that I ignore 90% of what the people I follow write, and I mostly follow people for updates/news/commentary rather than social contact.
But then I'm very aware that I'm very introverted. I like social contact in moderation, but it exhausts me, and every now and again I just get "social burnout" and turns into a total recluse for months on end.
What doesn't work for me about Snapchat is primarily that it is video. Video to me is "high touch" - it takes much more energy than writing a tweet, and similarly watching a video requires magnitudes more attention than rapidly scanning past a bunch of tweets.
I still don't get it.