Generally all contractors say "the next guys will take care of that". For example, when framing you don't really care if the studs are really straight or if the walls are square. The "next guy" will take care of that.
True enough, when I was drywalling I had the builder come back to take care of some bowed studs that should never have been used.
I've also volunteered at Habitat for Humanity and can confirm that very little "accurate measuring and cutting" was occurring. They'd quickly measure some things, shout out numbers, and then use a circular saw to rough cut it out. But that was it - they didn't refine it after that and went about their merry way.
I have to believe that the accuracy of a foundation is more important but I think it's a fool's dream. They get "close" and they're checked out before the "next guy" has to fix it.
Unless a 3d printer or CNC machine is responsible for the accuracy you better count me out.
The finish work is the final last guy. The guy that did our trim would randomly yell out swear words every 20 minutes. His life is hard. And he was expensive.
The latter can really kill a project if you can't get it right consistently, preferably first time.
That's where the skill comes in - not just the physical labour, but the experience needed to make allowances for material tolerances and other possible gotchas.
Professionals (should) have that knack, amateurs rarely will.