Flexibility to move the vFiler without VMware knowing... some even create a vFiler per datastore (can be overkill but any way you could group it for mobility with data motion). It works near the same as vFiler0 and each vFiler can have its own IPSpace separate from vfiler0 (separate routing table if needed). It can also be helpful when you upgrade to a new controller and new disks with data motion to move between controllers.