The FileSystem DashCopy workflow, different from LiveSync, was created to provide support for replicating files and shares of entities that do not have Commvault agent installed. You can specify any source UNC path (for Windows) or mount path (for Unix) and a corresponding destination path. The paths can be for a filer volume or even a local machine drive shared as UNC.
The workflow does not expect Commvault agent to be present. Hence it asks for the credentials for both the source and destination and saves it as a replication pair to be run on a schedule. When executed, it runs a workflow job that automatically creates a subclient for the pair, runs a backup, followed by auxcopy, followed by a restore.
This workflow was designed for filer admins who wanted easy control for replicating a set of files/shares outside of Commvault agents.