I separate mine into ziplock bags and number the outside with a marker showing how many times they have been fired. All my brass is fired the same amount of times since new. I shoot .223 and .308 in highpower and palma. Every round counts. When brass work hardens after so many times being reloaded, the "spring back" will be different when sizing. This can lead to different amounts of miniscule neck tension if brass is mixed up. Does'nt show up at the shorter ranges, but you will see it at 1000yds(IMO).
Geez, I sound like a damn benchrester.
Also, if you have a piece go bad on you, you know that the whole lot is ready to be thrown in the trash.