At first glance, it might sound kind of cool to watch a movie while playing a game while video-chatting with your friends while looking up stuff on the web while watching TV news - and all of that at the same time on the same screen. I personally don't consider it very practical and really don't see how that's supposed to be the next big thing in home entertainment, though.
It's more practical/useful for non-gaming situations. Alongside TV, movie or a fitness app 'snap' is a great idea (whether it's great in practice remains to be seen). Even casual games (PvZ2 with a sidebar seems fine to me).
In a core game? I don't think giving up peripheral vision in BF4 for a twitter sidebar is going to be particularly popular with players.