There should be a button to delete all read-only (not-checked-out) copies of files within the working folder.
Correct me if I am wrong, but I believe the Workspace Sync button only synchronizes the local files with those in Vault. It does not seem to remove files which were downloaded but not checked out. I would want a similar button, but instead of synchronizing the local workspace files with Vault, it found the ones that are not checked out and deleted them.
There are a lot of users who are just 'consumers' of the file and just end up with a local read-only copy that stays there forever unless they know to go delete the file from their workspace.