I could live with the locking or the corrupted repos if it was half decent at just sharing code, but daily we had problems where someone would check in code, VSS would say it was checked in but the person updating would get stale versions. Sometimes if you looked at the server version it be be correct but not what you would receive on a fresh checkout.
It was literally less functional than copying to a shared drive. Of course management and other developers refused to believe that OSS solutions were better, MS ecosystem developers were an extremely insular group.