Yes I did it too, but I mute the sound of the tennis.
As for the reason to watch a movie with music on, honestly I can't give you a rational answer, it's just sometimes I think watching a movie is a waste of time. I could do plenty of other thing at the same time instead of just being focused on a single thing, if you see what I mean !
I get it. It's like keeping your eyes busy, while your ears are.