
I am a big believer in prototyping. I think it has the potential to really help along any project, no matter what kind of development management technique is being employed. A quick disposable proof-of-concept can immediately bring an entire team onto the same page, illustrate design and interaction issues, and foster creative solutions.
At CP+B we have been focusing on creating interactive prototypes--essentially HTML wireframes--that help guide the creative process. It's easy to come up with an idea and even describe it thoroughly, only to realize that when you finally see it in action it isn't quite what you had expected. By producing simple clickable prototypes everyone can easily say "oh yeah, we hadn't thought of that." This provides for rapid iterations in both graphic design and interaction design early on in the process, presents to the client a much more polished product, and reduces development and QA cycles.