Lists the folders associated with updates from sources other than Microsoft Update. These folders can be safely deleted because ...

Lists the folders associated with updates from sources other than Microsoft 
Update. These folders can be safely deleted because they are no longer 
referenced by the WSUS server.

Notes: 
For MSI updates, you may want to leave the package folder intact because clients
that have installed the package will continue to use this folder for MSI repair 
operations.

WSUS provides APIs, but no UI, for distributing updates that come from sources 
other than Microsoft Update. The metadata for such updates can be removed from 
the server using the IUpdateServer.DeleteUpdate API, but update content is left 
behind in the package folder.

listunreferencedpackagefolders