It’s a feature that Microsoft was very late to rip off from other platforms. I’ve been using it in different Linux/UNIX graphical environments for ages.

You can think about it as a way to organize your windows by splitting them into groups. If you work on multiple things and require to have many windows opened simultaneously, you can make your desktop less cluttered. You can then switch between the desktop by swiping laptop touchpad (with 3 or 4 fingers), or hitting some keyboard combo.

I also use them kind of instead traditional task switcher. I’ve got one browser window maximized on workspace 1, fullscreen terminal on 2, mail and messengers on 3, even more apps on 4. It’s like multi monitor functionality with just one screen.