YouTube TV's new MultiView feature is like the old-fashioned Picture-In-Picture (PIP) found on some televisions. The biggest difference is that while PIP allows you to combine any two video inputs, MultiView only exists for whatever combinations that YouTube thinks are the most desirable, like the two NCAA basketball tournament games shown below. I didn't use it to watch to simultaneously watch these games, but if the game I was watching went to commercial (ridiculously long commercials), I would flip to the dual screen mode and watch the other game until I saw my game come back on. If both were showing commercials I would just mute the volume until one came back.
This feature was very recently introduced and not everyone has it yet, but should soon.