I will say this about chain, cog, ring, and rear derailleur pulleys…keeping the built up hardened gunk off them makes shifting more accurate. I’m not good about regular cleaning of those components. And, there have been times when my shifting starts to go wonky, or the chain will skip, and I think “Well, I need a new chain (or gear cassette/chainring).” But then I put the bike on the work stand and notice that I have significant gunk on the gears. I clean it off thoroughly, and shifting improves. I think the hardened grease gunk prevents the chain from seating on the various gears, and thereby disrupts proper shifting…like a worn chain would do.

Dan