I think alot of cyclists and fitters miss the biggest point. This is more with the so-called "shop it" and less so with a higher end fit.
What they miss is doing an assessment of you before the fit. Some higher end fiters will do soem sort of assessment then fit the bike to your imbalances.
I've posted an article on my website disscussing this(pelotoncoaching dot com.) .
So you get a fit based on what's wrong with your posture and any issues you have with mobilty, flexibilty,injury or muscular imbalance.
this does you little or no good and may lead to disfunctional movement patterns. Making the issues worse.