Firstly, Microsoft recommend headless for VM Host, but honestly, I think you are going to be hard-pressed to see that. The extra admin when you don't have a GUI is a pain. I suspect if you have a few racks full of servers doing live migrations, on the fly balancing load, etc. then maybe - but a single one. I really don't see it. If you look at the Linux model, where you load the GUID "sort of" afterwards, has very little impact on quite lowly hardware. Theoretically, according to the MS licensing, you are not really supposed to have ANYTHING running on the host, so should be minuscule.