You could have it duplicate the image, or use it like 2 desktops, or one big ass one. Duplicate would be handy if you wanted to monitor what someone was doing like at a business, or if you had a bud and were playing games, each could have their own monitor (that would be great). 2 desktops is obvious, have a report on one with the sources on another, and a big ass one...well I never use one big one but you could.
Granted the 2 desktops is really just called extended desktop. You can maximize to just one monitor though, or have it fit to both screens.