On my laptop, I use the external port VGA to conhanect to a beamer for presentations. I place the beamer "above" my laptop screen instead of cloning, because I think people should not see all my windows and the stuff I do.
This is how it currently works: You have 4 desktops (or more or less, let's say 4 for simplicity). Each desktop has 2 screens: the internal one and the beamer. On my internal screen I want to prepare things and do things nobody should see, on the external one I have a presentation (for example an okular presentation window). Now I switch desktops on the internal screen - and the presentation is gone, because it also switches desktops on the external one. This never made sense to me. I want to treat both my screens independently.
This is what I suggest: Switch the logic such that I have 2 screens, and the internal screen has 4 desktops, while the external one has ... let's say 2. I can switch desktops on the internal without changing what is visible on the external one and vice versa. Desktops on the internal and external screen should not be connected to each other at all, both screens should work entirely independent. IMO, this logic makes much more sense in any use case I can think of.
Please shoot your comments at me - or better, implement it and tell me how great the idea was