I've used it to put video from web based video chat on top of a full screen video, while still keeping focus on the main video. I mainly browse with a whole bunch of tabs open instead of multiple windows, so it's useful to pull a video out of a page and be able to navigate away and continue watching instead of dragging to a new window which would take up more space and get lost more easily. I've also used it for checking docs while following video tutorials, or watching recorded classes while looking at assignment pages.