Knowing reality tends not to be perfect, Jaguar Cars used software to manage the dimensional variations that occur in every manufactured part. Sure, these parts typically fit together, but Jaguar Cars wanted to know what affect so many thousandths on every part would have on the fit and finish of its new Jaguar S-Type luxury sports sedan. Dimensional variability, even in thousandths, is an anathema to assembly operations. The stackup in dimensional variability can make cars difficult to build and costly to rework. Fit and finish usually suffers.
Manufacturing can do just so much to manage dimensional variability.
It can spend more time manufacturing parts. However, the closer manufacturing gets to nominal, especially where small part tolerances are involved, the higher the costs to manufacture those parts. It can spend more time or add more labor during assembly to ensure fit and finish, but that slows production and adds costs. It can fix product after production. That just won't do, especially at high production runs.