I had a case once, where I wanted to use a SFML window in fullscreen on a projector (second screen), while I control the content from another window on my laptop (first screen). Currently this requires a workaround. Of course this is just one use case, that I could think of, but I'm sure there are more. Especially if you have some bigger setup. So I think it would be a good idea to extend SFML's monitor capabilities.