The watercooler / hallway discussions are the signs of a culture lacking documentation processes. If requirements or changes are communicated in this way what

The watercooler / hallway discussions are the signs of a culture lacking documentation processes. If requirements or changes are communicated in this way what happens when someone leaves or tries to QA the latest changes? What if there is a disagreement where one person assumed something else during the hallway discussion? Without documentation a company starts to fall apart after the team grows bigger than 6-12 people.