Writing increases your rate of revelation. This is true irrespective of the subject because writing is a process of reflection, assertion, and iteration.

Writing clarifies your own ideas. Writing begets new ideas too. Writing lets you explore ideas in depth even if you won’t have time to act on them all. Writing shows people how you think and lets ... See more

If writing down your ideas always makes them more precise and more complete, then no one who hasn't written about a topic has fully formed ideas about it. And someone who never writes has no fully formed ideas about anything nontrivial.