There's probably more,Mike, but I'm not noticing it much. In lighter shotguns, with unperfect form, a 12 pellet load can hurt.
And after maybe 20 years of shootng same in a Correctional system, I see very little a 12 pellet 00 load will do that a 9 pellet load won't.
IMO, except for very special circumstances, "Serious" shotgunners would be better off not using either 12 or 15 pellet 00 loads.
Magnum is an old Cherokee word for "Moneywaster"(G)....