I've heard that up to 80% of the torque you apply to a bolt can go to overcoming friction between the mating surfaces, rather than establishing the right preload.
That has merit with regard to the
threaded portion and under
head contact surface of the fastener, as any torque needed to overcome resistance can throw off the ultimate bolt torquing spec.
Machinery assembly (engines in particular) use a bolt
stretch measuring device, verses straight up torque values for that reason.
The grease or no grease issue is confined the the square tapered portion of the shaft in this bike case. There, I don't think the end result (w/grease or w/o grease) is significant. I wouldn't purposely degrease that surface, nor would I intentionally lube it up, but just clean the area of any debris. WD40 there maybe. Then a little oil on the threads or some anti-seize lube.