The extra snapvol hyve I believe is for the delta disk. It keeps track of stuff that changes and need to be removed after logoff if you don't have a writable volume.
And if you were to remark out the virtualize_registry my guess is that close to none application will work within Appvolumes. If you remark something out the Appvolumes filterr driver will not touch that specific part of Windows. We for example excluded almost all TEMP folders (see other topic) in the writable and applications do start up quicker but at the end you will always miss some stuff you need to virtualize. It's a matter of finding the perfect balance for your environment.
