This is something I actually use all the time. It helps to mentally separate the tasks I'm working on and keep things from getting cluttered. For example, if I'm editing audio on one desktop and preparing a 3D print on another, I can keep all those programs and files siloed into their own little workspace. I can also just stop working on either task at any point and just switch to a new clean desktop without losing my open programs and windows so I can just pop back into them later.