A competition neck sizing die (like mine from Redding) does not work the brass except the neck, nor does it pull the neck from the inside like a sizing button. Assuming theremaining aspects of your handloading technique are up to par, they tend to provide more consistency from round to round. If you are using a full sizing die, you work the brass every round and, depending how close to max pressure you are running, that can shorten brass life. This is mainly for bolt guns, as semi-automatics need to be full-size resizing every round to maintain optimum feeding and chabering capabilities. Some match chambers also need to be full-size resized every time to avoid pressure problems.
There are several handloading sites that focus on the extreme minutia of loading techniques - this is not the site for that in depth discussion.