The colleague who remembers old decisions can save a team from repeating an expensive argument.

Groups forget in a particular way. The reasons behind a decision fade much faster than the decision itself, so a year later the same debate opens again with all the original heat and none of the original evidence. The person who remembers why is doing real work, even though it looks like reminiscing, and their value only becomes obvious after they leave.

Write down the reasoning, not just the outcome, when your group settles something. A short note about what was considered and rejected saves whole afternoons later, and it means the memory does not depend on one person still being in the room.