I had gotten lazy over the last few years, and stopped lapping rings. I wasn't seeing any problems, and I hated the clean-up.
I was helping a friend mount a scope recently, and his attention to detail kind of woke me up, or maybe kicked me in the butt! I decided to go back and lap about ten sets of rings, ranging from Burris Tactical Extremes through TPS rings and up to Leupold Mark 4, Badger, and Vortex/Seekins.
The Badgers and Vortex/Seekins rings were close, but they still needed to be lapped a bit. I was really glad I went back and got it done.
The Burris and TPS rings really needed lapping. It looked like in some cases they were only making contact over about 25-30% of the inner surface out of the box.
The only rings that looked like they were acceptable as they came out of the box were a set of Leupold Mark 4's.
All of those rings had seen some use, and they all worked fine. I didn't have to do any serious trouble shooting with any of them. They weren't mounted on anything with too much recoil, .308 Winchester or .30-'06 tops, and a lot of that was loaded with moderate powder charges. But some of those rings weren't making that much contact, and after seeing about ten spooky patterns over a couple of days, I decided I will never skip that step again.
Buy good rings, but take the time to lap them. And lap the base as well. Even if it passes the tap test, it is probably not making full contact.
None of this is costly, none of it takes too long, and I think it is worth the time.