Our single use license holders cannot easily leverage our concurrent licensed extensions.
(They have to close down ArcGIS, load the Administrator, set the license to concurrent (leveraging our small pool concurrent desktop licenses), then use the extension. Once done with it, they again close down ArcGIs for Desktop, open the ArcGIS Administrator and set the license back to their Single Use license).
This is a moot point for those on a 100% concurrent model but we had purchased our licenses back when Concurrent Licensing wasnt a viable option (borrowing was not available pre10.x).
It would be great if we could have all of our Single Use license holders being able to leverage infrequently used extensions that we have on our license server without having to switch to a concurrent desktop license to do so.