There is a lot of abrasive grit and grime in the primer pocket. If you deprime before reloading and then clean, the tumbling media cleans out the flash hole. This prevents dirt and grime from falling into your reloading equipment. This allows the new primer to seat properly. A large percentage of misfires are due to issues with primers. Since the Deprimer fits multiple calibers, you save time by sorting cases by caliber as you deprime.