When an idea strikes, what do you do with it? The commonly-held belief is that you sketch the idea on paper, as a sort of refinement process. Why? Because ideas, especially visual ones, are conceptually rough and difficult to articulate. Sketching an idea on paper can be a process of refinement. Through sketching, an idea becomes sufficiently polished to warrant actual implementation.
However, there is another purpose to sketching that is often overlooked. Sketching isn't always about slowly shaping and fine-tuning a single idea. In Smashing Magazine's recent publication The Mobile Book, Dennis Kardys writes a chapter called “Hands on Design for Mobile” in which he points out this disparate purpose to ideation and sketching:
We often think of sketching as a way to generate and communicate ideas, but it can also be a weapon to dismantle them. The goal of sketching ... isn’t to produce drawings that inform the final design ... The goal is to drive out those stubborn, thorny ideas and make room for new ones. Only then can we look anew and achieve a deeper understanding of what we’re designing.
Sometimes you work with ideas like a mason works with stone. You start with a large, unformed block of stone and slowly chip away at it until you arrive at the finished product. However, sometimes you work with ideas like a farmer doing a controlled burn. You burn everything down to make room for new growth. Only then do you see anew things hidden beforehand.