Where you able to figure this out ?
In my opinion, the purpose is to have a separate emulated screen that you show to your video conference and where you only put what you want to be visible. This is usually done with a two monitors setup where on one you only put what you want to display, but maybe you only have one monitor or maybe you need one more, whatever, it's a separate screen and you will be only streaming this one.
How to use it, I don't know. I've only been able to send windows to it using keyboard shortcuts but then I can't interact with them because "my mouse isn't really on the window". I'm looking at how you could display it on your real monitor when needed but haven't found any information yet. If you've figured it out I would be really interested.