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