Architect/developer here:

A building is usually not very precise compared to manufacturing tolerances. Look at your counters and where they meet walls. The whole notion of trim and caulking is to hide these imperfections. Even with skyscrapers, you have to account for minor settling and expansion of materials.

Secondly, in terms of construction technique, you either have a plumb or a laser level to make sure you're building plumb and straight. In today's construction, you'll essentially pour your slab and the framers will draw in all the walls on the floors with a tolerance of about a 1/2". They then build straight, and level walls; even if the floor is wonky.

When the building is framed, other trades come in and work with whats on site as it is built. So, for example, you'd come in with window shop drawings afterwards and measure the openings. Then you'd shim and fit in your windows to roughly the opening, and the waterproofing/cladding will work with what is there, and cut things on-site to make sure it more-or-less fits, rather than whats on the plans.

That's why ever subcontractor hates each other. The guy before you installing things can really mess up your contract.

TL:DR; its accurate enough to be hidden with trim/joints/finishes, but also lasers.