Cleanliness is a great thing. Arguing that varnish is good because it increases engine temperature leading to lower emissions is a stretch, at best.
Rings that aren't sticky, good oil flow through even the tiniest oil channels, tick-free lifters, properly operating variable valve timing systems, efficient heat transfer where such heat transfer is supposed to exist, properly conditioned seals without crusty coatings and lack of hot spots due to unplanned insulation are all great things to have.
Does not having them mean that your engine will explode? Of course not. But there's a difference between "still on the road" and "still like new". Although far from new, I drive a 'sporting brand' (BMW) and I drive it in a style consistent with its design heritage. For all of my cars I endeavour to keep them as "like new" as possible, for as long as possible, while still financially feasible. I'm not rich and there are certain financial realities limiting how far this "like new" thing can go as the car ages. Doing all my own work enables me to go to farther extents than some with the cost savings - this includes suspension, bushings, interior gear, detailing and power train. (as an aside I see people claiming to have 250k mi on their cars only changed batteries, brakes and a starter and have 'no issues at all' - highly, highly unlikely. Hard things get soft, soft things get hard, and they all wear out. Different topic though.)
I strive for a higher standard than simply passing emissions or safety inspections and staying on the road. It's partially a hobby, partially pride of ownership, and partially because I push the car from time to time. It stands to reason that cleanliness is of value to me. I don't like unnecessary noises or harshness and I value maintaining original performance, emissions compliance and fuel economy as the years and miles go by.
