Will Evans discusses how he uses wireframes in his design process. The story is one you've probably heard before. It's a description of concept design, using wireframes as the tool for finding the right design. One could use sketching just as well.
He's talking about that path we take as designers to frame the problem for discussion, extrapolate solutions from that discussion, and generate possible solution concepts. He calls his process one of divergence, transformation, and covergence. This maps to a common cycle in design where there is a lot of front-loaded generation of ideas and further and further reduction of solutions as the process unfolds. There's a great diagram in Buxton's Sketching the User Experience on page 146 (based on Pugh's 1990 work, Total Design) which discusses the waves of expanding and contracting generation and reduction that happens as designers find focus. The right design emerges at the end of the process of ideation and selection.
It's interesting to read Evans' description of his thoughts during his design process, as it mirrors what Buxton and Pugh describe. We need to hear more detailed accounts like his, that fill in the picture for other practitioners, and hopefully impress upon some of us different ways for practicing our craft.
http://blog.semanticfoundry.com/2009/01/01/shades-of-gray-wireframes-as-thinking-device/