Every conversation in a meeting becomes ambient knowledge that lives in the heads of the people who were in the room. Every written decision becomes durable knowledge that lives forever and scales to everyone who joins later. The compounding advantage of writing things down is the single biggest operating leverage a growing company has.
What to write down
Decisions, with their context and the alternatives considered. Why something was built the way it was. Why something was killed. The reasoning behind a pricing change. The plan for next quarter, with the trade-offs that produced it. Almost anything that took thinking is worth writing.
What you get
New hires onboard themselves. Decisions stop being re-debated every six months. Async work becomes possible. The company stops depending on the founder's memory. The best leaders compound their thinking through what they write; everyone else has to be in the room to receive it.
The shape of good writing
Short enough to be read, complete enough to stand alone, dated, searchable. Not perfect. Done and shared beats polished and private every time.