プロトタイプとは何ですか？

The most obvious difference between these two manufacturing technologies is that 3D printing is much cheaper and is capable of building geometries that are impossible or impractical to machine, such as curved deep holes, interior square corners or fully enclosed hollow sections. CNC machining, on the other hand, offers speed and accuracy.

For initial, low-fidelity prototypes 3D printing is a popular choice. WIth the cost of entry for a 3D printer being a fraction of the cost of a CNC machine, product developers can save a lot of time and money by 3D printing their non-functional iterations on a 3D printer. 

 A major point to consider when designing and 3D printing prototypes, is that sometimes the geometries and features that can be 3D printed do not translate well when it comes time to CNC machine the part.