If you’ve ever used a multiple monitor equipped PC, then you can imagine how Multiplicity works. Each monitor is connected to its own PC. When the user moves the mouse over to a given monitor, the user is then controlling that PC.
Multiplicity is not a “remote desktop” application. Each system continues to need its own monitor to display that PC. Multiplicity is used to seamlessly move between multiple machines (and their monitors) and control them from one primary PC.