In System Center Virtual Machine Manager 2012, you have the option to modify your Guest OS settings when deploying a new virtual machine. The settings you can modify are things like the product key, local administrator password, etc.
One other thing you can define, is that fact that the new virtual machine has to be joined to the domain. Very useful. But what if you also want to define the default Organizational Unit this machine has to be put in? Well, that can also be done using the Guest OS Profile.