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se1derful
You'll struggle to notice. Ever since SIS became a thing, Shimano has rocked the Centeron-G jockey wheel (only the top one is called a jockey wheel BTW, the other is the tension pulley). This has taken the form of a slightly wider bushing than the pulley which has a metal insert for its own bushing in the cheap seats, the same deal in ceramic for 600/Ultegra, and a super fancy little ball bearing cartridge in Dura-Ace with built-in lateral slop (I guess it must be a pair of races of tiny balls for it to work).
Aftermarket replacements have made that all look silly by just having thinner teeth on the top pulley, or made it look even sillier still by not even bothering with a difference. I think Shimano must have decided back in the day it's an important component of SIS, helps the HyperGlide do its thing, and maybe it really did in the 6s days, but I've mucked around with eliminating it on 7s and up, and never noticed much change. I guess maybe it's a little more tolerant of bad adjustment, but I can't see how it won't inescapably make the chain less responsive to the RD.
I'm actually rocking narrow/wide 12/14t in my 11s Di2, and it's totally fine, probably a bit snappier than stock even (at the cost of a smaller correct adjustment window).