Depending on the application, the above is correct.
I've 3 rifles in an 06' case . 1 must be full lengthed every time, they won't chamber otherwise. In the others sizing just half of the neck improved groups by a visible margin. The thing in those 2 is that 1 has a chamber that is correct at the neck base but is long from the base to the shoulder and the other just has a fat shoulder. Now its only say .002-4 on each, but full sizing each time reduces case life from 10 loads to 5 in those 2. In 1 of the 3 the half necking gave me group reduction w/a good load from 2" to 1" and allowed me to move the velocity up by 100fps and keep my 1.5" 100yd hunting load group.
It is really a gun to gun thing. If you have a tight/minimum chamber you wont see nearly the group or case life change that you will see in 1 that is near maximums or that is on the long side of the headspace range.