Every time someone moves to a new computer and has to reinstall Vault, they have to remember not to accept Workspace Sync's default settings, which will delete old files in their workspace that have not been checked in yet.
Users will inevitably keep important files in their workspace and forget to check them in, and they will inevitably click "Finish" in the Workspace Sync window without looking at what it's doing to their files.
This feature absolutely needs to be opt-in. This is far too dangerous to be the default setting.
