Prototyping: Making a sample of an initial idea often reveals something about the idea that could be simplified or improved. A sample may reveal flaws that can't be deduced from a sketch. Prototyping iteratively, compared to sketching iteratively adds testing and interaction with and manipulating the design at each step. While not every product needs exhaustive modelling the best way to discover an unconsidered function or flaw is through iterative actual (not virtual PC) modelling.
3D printing is one way to produce samples of a product idea. I've had an idea for a jig that could be used to help install another hardware product I invented. My initial idea was for a jig with a critical variable fixed in position. Once 3D printed I was able to test the initial jig idea, and it revealed to me the value of making that fixed detail into an adjustable detail. A new prototype was designed and printed that allowed the position of the detail to move. It revealed that a way to lock the detail into position would eliminate the need for an accessory clamp to hold it in position. A third prototype was printed to stiffen up the back plate of the jig. It also modified and simplified the insert end to ease insertion and get out of the way of the drill bit being used. It is not unusual that it takes 3 or more prototypes before homing in on the best solution. Often the early prototypes reveal opportunities for improvement that weren't obvious or initially considered.


