I haven't been doing it. I just heard several people suggest and I read it in a couple of manuals. However I've just been loading the same amount regardless. Since I'm mainly reloading for just bulk ammo and not being real precise for accuracy ( but better consistency than shelf ) most of what I'm loading now I just haven't bothered with it.BHPSteel beat me to it.
This another nugget of Fuddlore. The specifications for cartridge brass for 5.56mm and .223 Rem are the same. There may be, MAY be very slight almost immeasurable variations in mass produced brass among multiple manufacturers, but you'd have a hard time measuring them.
If you sort your brass by headstamp, do it for continuity and consistency in case volume, not because you think one is thicker than the other due to "higher pressures."