Consider a company like www.hahnandwoodward.com (now Hahn-Vorbach & Associates). They focus on restoration of very rare cars (like the Mercedes 300SL Gullwing). They are starting to use 3-D scanners for a variety of situations.
For example: A client brings in their 1 of 1 roadster or a concept car that needs restoration. There aren't any easily accessible plans or drawings, so you take a 3-D model of the car to convert it into an engineering drawing that you can use to plan your restoration or modification. You could run into a situation where it just isn't possible to replace a broken differential because there was only ever 1 made, or maybe the client wants an upgraded differential. You can use the engineering drawing you built to see if you can fit a part that is currently in production. The current method without 3-D scanning is to take a lot of careful measurements or attempt to see if a part will fit. In the end, it's risky and easy to make a mistake.
Consider another situation where maybe the car comes in with some previous bodywork. Sure, everything lines up NOW, but that is because the previous mechanic just bent some things so they fit together. If you don't know this going in, you could buy the actual correct part (lets say a fender) and discover that the NEW fender doesn't fit because the frame of the car is off-kilter. You could avoid this by taking a 3-D scan of the car in its current condition and using that scan to determine if the existing car matches factory conditions.
In short: Anytime you need to do custom work on an existing product or when the product itself is custom (like an old farmhouse) taking a 3-D scan of the place can be very useful in planning out your work or retrofit plan.