Again from Smarter Than You Think:

Audiences clarify the mind even more…. And suddenly all the weak points to their argument, their cliches and lazy, autofill  thinking, become painfully obvious. Gabriel Weinberg, the founder of DuckDuckGo…writes about search-engine politics, and he once described the process neatly:
Blogging forces you to write down your arguments and assumptions. This is the single biggest reason to do it, and I think it alone makes it worth it. You have a lot of opinions. I’m sure some of them you hold strongly. Pick one and write it up in a post–I’m sure your opinion will change somewhat or at least become more nuanced. When you move from your head to “paper,” a lot of the hand-wavyness goes away and you are left to really defend your position to yourself.

– Clive Thompson