Metro-X defaults to a single-screen setup. The first screen configured is labeled Screen 0. When you add a second screen, all of its configuration default settings will duplicate the current settings of Screen 0. So if your hardware is the same on all screens, you can save time by configuring Screen 0 before adding the other screens. Similarly, as more screens are added, the settings of whichever one is currently active when you add another screen will determine the default settings of the new screen.