Never bother. I think the even carbon coating on the inside of the neck gives a more uniform neck tension. Ran a few tests a few years ago regards inside neck cleaning. After over 150 rounds of firing; I could tell no difference between a clean inside case neck and one that had a good many firings through it.
Ya know, there just might be some useless efforts out there that we needn't bother with. Of course legends and habit usually rule the roost.