I think better when I write, and I write better where I can re-read and edit my thoughts.
Fixing ideas to the page is uncomfortable and valuable, because the author confronts themselves with the previously invisible incoherence, incompleteness, and contradictions of the thoughts that flowed through their mind.
Writing automatically forces the author to give reasons for their statements, and then justify themselves when additional facts or new contexts make them wish to change their view or update their beliefs.
makes it more difficult to hold incoherent or contradictory views, and helps me deliberately distinguish what I really think.