I agree with both points of view. If you are getting the accuracy and velocity results that you desire and you don't feel the need, then there probably isn't one.
I neck turn all my brass. I chamber my own barrels and specify my own reamers. I spec the reamers "snug neck", meaning that factory rounds will just barely/safely fit. I rarely full length resize my brass at any time throughout it's life. The brass will tell you when it needs it by sticky bolt lift. I weight sort my brass and it lives with a specific rifle for the life of the brass. I only have to neck turn new, un-fired brass once. I prep the cases by doing both sides of the flash holes, the primer pocket, OAL, inside and outside neck chamfer. In other words, the brass is perfect once all of that is done. I shoot Lapua exclusively. For those of you who say it doesn't need it, I would agree, for the most part. It's pretty damned good right out of the box. I weight sort my brass because I am looking for the best of the best. I usually retire my brass at 20 firings, so my (per firing) brass costs are ridiculously low.
I either buy Wilson neck sizer blanks and finish them with the same reamer, or if I'm lazy, I'll buy Wilson finished neck dies. I would suggest that if you are going to go to the extent of neck sizing, that you should neck turn, if for no other reason than consistency. You can always adjust the sizing of the neck by buying a different sized button.
Neck sizing will not turn a 1 MOA round into a .1 MOA round all by itself. It's all the small things, including neck sizing that add up to improve consistency in the direction of .1 MOA. If you are getting .3 to .5 MOA without neck sizing and are happy with it, then by all means, stay that course and don't let anyone tell you there is anything wrong with that, because there isn't.
edit; I should also add that I don't shoot PRS, or anything along those lines. So, losing my brass in those kinds of comps isn't going to be a factor. I just shoot single shot, off of a bench, I supposed "Fudd style"