In the early stage of new product development, it never lack of one process —Model Making.
When designer completes the work 3D CAD model in computer with engineering software, you can see it clear from computer. But you can not touch it, so prototype model is in need. Here we say model is physical prototype, you can see and touch it.
Now rapid prototyping model can be made by many methods, for example: SLA, SLS, CNC machining, 3D printing, and so on. After finished model, designer could check the dimensions, thus, they will know if the product size is correct. And test the structure if some shapes need to be changed. To avoid the risk of creating mold directly.