In the old days, prototypes was built with wood, fiberglass and a lot of bondo! And it required a lot of manual labour and if there was any changes to be done, well you had to basically start over.
Nowadays prototypes are created in advanced computer software, where pictures and close-up details are created with photo realistic quality. So no need for expensive prototypes at this stage!
In a modern CAD/DCC software you work in 3 dimensions. The advantage with this is that pieces and parts can be matched before manufactured and thereby eleminating expensive manufacting. The 3D model can then be used as base for manufacturing or/and as an marketing asset with photorealistic pictures, animations, technical illustrations for assembly... The list goes on.
A product is often produced in different colors, sizes and materials. Copying and alter in a 3D software is usually a very quick process and changes are made fast.
The technology makes the workflow much more flexible than with traditional techniques. This makes digital methods much cheaper and efficient.