When you neck ream, you are removing brass from the inside of the neck of your case. When you are neck turning, you are removing brass from the outside of the case. With the neck turning, the brass is trued, as in, all inconsistancy is cut from the case. This in turn, causes your bullet to release from the case with more consistancy. For hunting purposes, this isn't really necessary, but for bench rest, that extra 1/4 inch of accuracy could be the difference between winning or losing your match. If your fired cases neckswill easilyaccept a bullet before you resize them, then neck turning is unnecessary. If you can't get the bullet in the fired case, then the turning is an option.