The main benefit of a hypervisor is to enable you to run multiple OSes simultaneously on the same hardware. That's the bottom line.
Since I am an IT Consultant/MSP the Microserver forms part of my test lab for developing/testing solutions that I would deploy at a customer's site.
If all you intend to run is WHS 2011 on it then there is no need to run a hypervisor etc.
On mine at the moment I have WHS 2011, Windows 8 Client, SBS Essentials 2011, and an Ubuntu client running Ubiquiti Unifi controller

Not all of them are running at the same time at the moment.
Without virtualisation I would need a separate box for each of those OS'es.
The other benefit for me is that once I have tested/proved a potential solution, I can document it so that when I come to do it at a customer site I'm likely to do it right first time. Massive benefit for me as a one-man band