Another reason for tight necked chambers.
Consistency in all aspects of handloading will help promote the very best accuracy that can be obtained from a rifle. Bullet release tension is important. It cannot be consistent if some case neck walls are thicker than others or if portions of a case neck are not the same thickness. If all cases have the same neck wall thickness then the bullet release will be more consistent shot to shot thereby helping to promote accuracy. It is part of a larger overall discipline.
I would like to mention that the individual can decide on how much neck clearance is right for their needs. It is dependent on the specs of the reamer and the original wall thickness of the chosen brass.
I have many rifles that I will use hunting with .003 or.004" per side neck wall clearance for bullet release. The tightest clearance I have hear of is .00035" per side. It was Virgil King in the article from Precision Shooting entitled The Secrets of the Houston Warehouse. It was chasing perfection in the BR game. A very interesting article!
Secrets of the Houston Warehouse
"Virgil did not size his case necks. With about .00035" clearance on all sides between the loaded round and chamber neck, the natural spring-back of the brass, in combination with his neck preparation, correctly gripped the bullets."
I made a 30 BR Long by plunging a 30 BR reamer approx. 1/2"deeper into the chamber to headspace as a 308. The design essentially grafts a 30 BR “top end” to the .308 Winchester case. The neck walls were turned to .0105" for a .0005" neck clearance per side. (1/2 a thousandth per side) I was able to reload without any sizing of the brass. There was some springback of the necks that held the bullet for single shot only. I could seat the bullets longer than the distance for contact with the lands and cam the bolt shut to have identical lands to ogive relationship. Some call this soft seating. Only thing I did was to carefully remove all carbon with fine steel wool and keep the chamber neck clean. I got the exact same accuracy as brass turned to .010" with more bullet release clearance of .001 per side that the necks had to be sized with a bushing die. It was fun but not a rifle I'd use for hunting.