Remove Unreferenced Data
If you select your backup plan in the main window and then pick “Remove Unreferenced Data…” from the menu, Arq uses its database to find all objects in the backup set that are no longer needed by any backup record, and deletes them.
Arq removes unreferenced data at the end of every backup activity, but if you delete some backup records and just want Arq to remove the data that become unreferenced as a result without doing a backup, pick “Remove Unreferenced Data…” from the menu.