I always lap ALL steel rings. I will admit it is like most things we do, its voodoo. Can't swear it helps, but it eliminates one more variable. And it can't hurt.
Of course this is if it is done right. I have lapping bars for 1", 30mm, and 34mm. I start out with a 200 grit, then 600 grit and finish up with 1200. When done, you can lay a scope or the lapping bar in the rings, shine a light and not see any gaps.
As far as any of the mount manufacturers claiming their rings are perfect, Bull. When they start making them to Aero Space tolerance, we could not afford them.
I have never lapped a ring that did not have high and low spots.
JMHO