"Writing down my design decisions enables me to:
Solidify my design approach: Within application design, there is a tendency to locally optimize (per feature, per screen) interactions and information displays. When you go back and articulate why those decisions were made, application-wide patterns often emerge that enable greater consistency.
Articulate my rationale: Designers need to explain how their solutions address business and user needs as well as how they address technical opportunities and limitations. Writing out your design rationale requires you to compose the story behind your product vision. That story is invaluable for communicating your design to stakeholders.
Ensure clarity: If you can't easily describe how an interface or feature works, chances are users will have a hard time understanding it."
Luke has a great point. Writing things down is simply a way to capture knowledge that's in your head. But because your writing is intended for other people to read, the process of doing it forces you to slow down a bit. As you work on the flow of the document you start to process it the way a beginner would. This can help you identify gaps in your thinking you may not have seen before.
We do this intuitively. We all know that taking five minutes to make a simple to-to list can help you organize your thoughts or your day.
Career coach R0bert Gatling says "write it down" was one of the best tips he ever got.
This is also one of the reasons having a blog can make you a better manager. By writing down your management philosophies and recording your best management conversations you can make your blog a database of best practices and ideas.
And yes, the picture is a random page from my sketchbook.
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