IDEO designer Keaton Herzer has written a terrific blog post titled, "What the hell is Rapid Prototyping?" Here's an excerpt:
It implies that there is an alternative — slow prototyping. I’m not aware of any design team that practices slow prototyping. That would be a waste of time and money for everyone and thatis super obvious. Let’s remind ourselves what the purpose of a prototype is: to test our ideas! History and statistics tell us that our ideas are wrong MOST of the time. So most of our prototypes will get thrown out after being invalidated. If that’s the case, why would we do anything but prototype rapidly? If you’re going to build a prototype — build it. Then test it. Then learn how bad your ideas were. Then do it again. I guess you could do that slowly if you wanted to, but I don’t see the point. There is no such thing as “rapid prototyping.” There is only prototyping — and you should be doing it rapidly.
I think slow prototyping does exist though, and it's not a good thing. Consider how large companies engage in what they consider to be prototyping. They build a mock-up of a potential new product. However, they take quite some time to do so. They try to make it as "beautiful" as possible, as free of imperfections and problems as they can imagine. Why? They are actually trying to validate an idea that they have. It's a demonstration to others in the organization, often used to solicit resource commitments. It's not actually prototyping. Why is it slow? They do not want to hear lots of criticism. They want positive feedback, so they take lots of time to make it as "good" as they can. To me, that's the type of slow prototyping that does exist in many organizations, and it often is counterproductive. It inhibits learning and adaptation, and thereby prevents the type of rapid improvement that Herzer describes.