Present windows could be used not only to switch the active window, but also to keep an eye on multiple (eventually full-screen) windows on the secondary screen while working in (an)other window(s) on the primary screen.

Use case: you have a social network in a browser window, an e-mail client, weather forecasts in another browser window and LibreOffice Writer in a fourth window. You want to work with full-screen Writer on your primary monitor, while keeping an eye on all the other windows.
You could tile them, but - by resizing the windows - you wouldn't see all your contact list on the social network, the whole weather forecast page, informations about your e-mails and so on.

Using Present Windows just on the secondary screen, perhaps without the windows' previews being grayed out (as it currently happens), would let you see  all your windows and zoom in one whenever needed.

Reproducible: Always