There are two basic use cases:

1. There are two live sporting events I'm interested in watching at the same time. I can pull them both up and when one goes to commercial or is at halftime, I switch to the other.

2. My wife is watching something, and there's a game on that I want to watch. I'll let her watch her thing with audio and I'll watch on the other half without audio (because that's the kind of guy I am.) This obviously changes if it's a playoff game or whatever.