What organisations lose when people leave is rarely documented. It lives in conversations nobody thought to preserve.
Organisational memory is the accumulated understanding of why things are the way they are. Why a project changed direction. Why a policy exists. Why a particular commitment was made to a particular customer.
Almost none of it is written down. It lives in the working memory of the people who were in the room, and it leaves the building when they do.
The cost is quiet but constant. Teams relitigate settled decisions. New managers inherit relationships with no history. Good work is forgotten at review time because the person who witnessed it has moved on.
Preserving that memory does not require surveillance. It requires a consistent, transparent record of the conversations people already agree are important, connected in a way that makes the past easy to consult.