Beware, this may sound like a very noobish question! Why does SFML (and many other game dev libraries) offer a way to create multiple windows? I never saw a game with more than one window and honestly, as a beginning game developer, I can't conceive of any way I might use more than one window.
Are they used as separate game views/states (in-game, main menu, pause menu, etc)? If that's so, how do you switch between windows seamlessly? Why not use the same windows to draw multiple states?