I've searched for reasons and couldn't find much. The fact that a website can know where a browser window is located (window.screenX/window.screenY) and that clicks position can be reported in that coordinate system sounds insane for a desktop. TOR Browser seems to spoof screenX and screenY to avoid fingerprinting.

Has anyone seen good use-cases for that feature? I'm thinking about dual window applications that interacts with each other (I think I saw a demo of something like this a while ago on HN but I wasn't able to find it again), or sites where behavior depends on their location on the virtual screen.