At work I'm trying to do more testing on virtual machines, and I've run into the thing where you have to "activate" a virtual Windows install, but you can't just use the key you used for your real system because Microsoft will think you upgraded or replaced your system and stop recognizing the real one (or something: I'm not exactly sure how it plays out).
It appears that technically you need a separate Windows license for each virtual machine you run. Which I totally understand from a technical perspective—if your OS's licensing is linked to the hardware it runs on and you run it on virtual hardware then you need to license it for the virtual hardware—but not at all from a business standpoint.
So it would all make sense, except that apparently newer versions of the OS allow you to run some fixed number of virtual installs (like ten or something) on the same license as the host OS. Whatever effort was required to implement that feature presumably exceeded the effort it would have taken to allow any number of virtual machines to run on a machine under a single host's license.
I literally cannot imagine a single reason for limiting the number of virtual installations of an OS under a single host's license. How is running a zillion copies of Windows on the same hardware going to cheat Microsoft out of anything?