When it comes to design, I maintain the philosophy that just about everything is a prototype, until it isn’t. That drives a lot of people nuts because most of us just want to see the finished goods. If you’re part of a broader team, you need to see some sausage making in order to make informed decisions.
Prototyping as a term can be as useful as it is problematic. It’s vague and open to too many interpretations – kind of like design. In cases like that, I find it’s better to use an analogy to tell people what you mean.
I recently started using the analogy that “prototyping is like sketching” to explain my philosophy. Trouble is, people misunderstand sketching too. When people see a sketch, they think, “unfinished”, but completion isn’t even the point of a sketch. Sketching, like a prototyping, is for communicating something vague not concrete. Why would you want to do that? One good reason is to explore your options with others.
Beware, most people don’t appreciate the process of moving from ambiguous to precise. “Done” is often rewarded over useful and usable. Ultimately, it comes down to the context in which you present things to people. No one likes to see unfinished work, but they do like to explore options.
 I want to give credit where credit is due. This dawned on me while attending a workshop on sketching for product design by Kevin Henry, an associate professor at Columbia College.