as the saying goes, "writing is thinking."
first, i don't try to write. i am not a writer. i don't have an editorial calendar, or a monthly post quota. i also don't attempt to hit a certain word count, or do keyword research to "optimize for SEO." very few of my essays rank:
what do these have in common? nothing. and that's the way i like it.
i don't have a journal for business decisions per se, but i do keep a monthly log of business highlights. each of my major project has its own Google Doc, with updates written in reverse chronolical. here's the format:
intro - share brief sentiments from the previous month
product updates - usually new features
acquisition - recap of tactics to increase topline exposure
activation - tactics / measurements from onboarding experiments
retention - same as retention, but for adding value to long-term customers
revenue - promotions, up sells and cross sells
referral - strategies implemented to encourge more word of mouth
team - changes in composition (promotions, hirings, firings)
metrics - sales, profit, etc
this log helps me reflect on my past 30 days' performance and commit myself to new experiments or decisions in the upcoming 30 days.
not much differs from what i think vs what i share. there are always some "private" details, such as sentiments about personnel, insights regarding managing other humans, etc that i don't share. but this not for lack of will -- i simply think it would be embarassing for colleagues if i "aired our dirty laundry" without consent.
to answer your question -- reading has impacted my business decisions more than writing. but i think writing is a necessary component to reading. whenever you read you fill up your head with ideas. writing helps you work those ideas back out of your head and into action.