BYOD (bring your own device) is the big noise in corporate IT, has been for a while. Now, it started with iPhones and macs and iPads, but if your staff have, for example, a Surface Pro 3 they like to use, you want some way for them to be able to use it in the corporate network environment, right?
Now, I'd question whether the right way to handle that is to join it to the Windows domain (I'd question whether having a Windows domain is the right way to handle ANYTHING in fact), but it's definitely a part of the corporate IT landscape nowadays, and MS should have some sort of a story for how you can do it.