I have several scheduled tasks that are full backups to an external (USB) hard drive. I used to include verification in the backup, but that made the backup take a long time to complete. Finally, I removed verification from the scheduled tasks, and performed it as a separate step. I wasn't surprised that the backups took less time to complete, but what surprised me was how much faster it was to do the verification afterwards. Doing the backup and the verification separately takes less time than doing them together, thus 'addition by subtraction'. I'd be interested to know if others have had the same experience.