The record everything is checked back to.
DRAWINGS · PLANS · SECTIONS · SCHEDULES
Drawings, plans, sections and schedules — the contractual record every model is checked back to.
However sophisticated the model becomes, 2D is where the contract lives. Drawings, plans, sections and schedules are the record everything else is measured against — and the one deliverable that has to be unambiguous.
Get the documentation right and the rest of the BIM stack has a reliable datum. Get it wrong and every dimension above inherits the error.