One "saves" the desired monitor type to the emulator. The physical monitor is needed for this. As soon as the monitor is "saved" on the emulator, a connected monitor is no longer needed on the emulator. The emulator then "simulates" the saved monitor.
The attached instructions describe the process of how this is done quite well.

Yes, it works. I use it on a Microsoft Surface and have set the external monitor (which is now unplugged) as the primary monitor. The Surface display is therefore no longer lit up and I can control it via Teamviewer.

How is the question to be understood? Should the monitor remain plugged into the emulator and simply be switched off?
If the emulator is programmed, the monitor can be removed and the emulator will simulate a switched-on monitor.