Obviously there's a wide spectrum of possible uses and different people have different "focus" tastes. I've found Firefox's PIP particularly useful in watching videos while grinding in certain types of MMOs. So long as the MMOs support "Borderless Window Fullscreen" rather than "pure" fullscreen, Firefox's PIP shows up right on top. I just recently upgraded to an ultra-widescreen so I've got plenty of horizontal space to play with. In a previous dual monitor setup I might have just had the game on one screen and the show on the other. This PIP gives me a bit more flexibility than that, especially I discover which games sing in the "2k" fullscreen. Some of these MMOs I didn't realize quite how cramped they felt in 1080p until I got to extend them to ultra-wide.