Works in low fidelity. Jerry writes his jokes on a yellow pad with a blue pen, and authored every episode of Seinfeld in long-hand in this way. This is like the sketching stage of UI design.

Why write/sketch instead of type/wireframe? Well, there might be a clue in the way Jason Snell talks about writing on the iPad:

Using the iPad slowed me down and got me to think about what I was writing in a way that using my trusty MacBook Air never would.

He likens it to the difference between writing with a pen vs. writing with a keyboard:

Writing with pen and paper felt appreciably different from typing. My mind would try to race ahead, but my pen could only go so fast. I ended up considering every sentence, every word choice, with greater care simply because I couldn’t dash it out and move ahead.

So maybe that’s why there’s so much value in sketching with pen and paper as well. Lines are imperfect. You can only go so fast. Making a mistake can be costly if it means you have to do it all over again, so you take your time to consider design options.

I’ve slowly started moving away from wireframes, and instead now prefer a workflow that includes several rounds of sketching, followed by prototyping in Axure. I think I get better results that way, and maybe the reason is that sketching slows down the mind just enough to do better work.