i think just on the china made engines guy's have been changing the ring,me included.FB rings are made from a softer cast material and seat better on a not so well machine cylinder.also his ring gaps run from .001-.003 at the largest,the biggest gap i had from any of his rings was a tight .002 and you always get more compression with his rings. the china made engines or any less quality, high dollar engine can run from .014 to .030.they also have a lot less tension on the cylinder wall,makes a smoother running engine.as far as opening up a new engine for me it is always better to start off with a new cylinder along with a new ring,no wear patterns from the ring before.
not so sure if they are needed on a better built engine like 3W,DA,Brison,BME.