Common sense should dictate that, I'm afraid. The basic idea is that you want to be able to do something without being dragged entirely out of one experience and into another, as it's done on the 360. This offers a way to have two distinctly different experiences going at the same exact time with the user being able to seamlessly interact with either one. I don't need some canned, and badly acted demonstration of how it can be useful. I already know how, and Microsoft themselves have already shown some of the ways it can be used, conveniently accompanied by bad acting.
Watching a football game? Maybe you want to snap fantasy football, or head to espn site to take a look at scores. Playing a game, want to stop and tell some people on twitter about it? Snap twitter, tweet, and then go back to your game. I mean, it's so easy to find how it would be useful. You can even Skype and chat with a friend while you're busy editing a video in upload studio. You and a friend can both be watching the same movie on your xbox ones, but have a Skype video chat open on the side so you guys can talk about what you're seeing. You are playing a game of killer instinct, and then you can snap and start a twitch broadcast is the way I believe that worked. Or what's to stop you from twitch live streaming a game of Ryse SP? Microsoft has already shown a multitude of ways for it work. The rest is really up to common sense after that.
You've not said anything anyone else hasn't already said, thought of, shown on stage or in a video.
I still don't want it. I have a phone and a tablet. If I'm watching the F1, I have the F1 app on my tablet. I can also switch to GAF to comment in the thread about whomever Maldonado just took out, see some GIFs, see the latest outrage over developer y saying platform z is 0.03% -/+ than we thought, in my hand, while my TV is showing the race without any empty space. It's fast, it's so easy that a pre school child can do it, its convenient, and I always always get what I want when I want it.
If I want to Twat about the game I'm playing, or watching, doing that on my phone or tablet is again easy, fast and convenient.
I've tried, but Snap has been shown to do, and I cannot imagine it doing, anything that is better for me than the options I already possess. It truly is a solution to a problem I do not have.
But that's just me.