While searching for data on another matter, I stumbled across this at the Blue Sheepdog website:
Repeated cycling of ammunition can lead to a critical failure according to a training bulletin released by the Gwinnett County (GA) Sheriff’s Department.
According to the bulletin, a Gwinnett County police officer’s pistol failed to fire in a deadly force situation. The officer executed a “tap-rack-bang” drill to get back in the fight and successfully resolved the encounter.
The round was returned to the manufacturer for analysis. They determined the primer had been rendered useless due to the cartridge having been cycled through the gun multiple times. An interview with the officer determined he unloaded his pistol when he got home every night, meaning two rounds were repeatedly chambered as many as 100 times each prior to the incident.
I've probably done hundreds of cycles of some rounds, and never had a failure like the one described here. On the other hand, why take chances?
Ammo used for defensive carry, if unloaded and loaded into the chamber on a repetitive basis, should probably be swapped out at some point and held aside for target practice.