When we reach for it
Runbooks, architecture decisions and handover material, where the client’s own people will maintain them afterwards. It is the documentation that has to outlive the engagement, so it belongs where the client’s own people already work rather than anywhere we would prefer.
When we would argue against it
Documentation that belongs beside the code. Anything that goes stale the moment the code changes should be in the repository. A page describing how the code works is stale the week after it is written; that belongs in the repository, next to the thing it describes.
What it looks like in delivery
Handover written where the people taking over already look, not where it was convenient for us to write it. Architecture decisions are recorded when the decision is taken, with the options rejected and the reasons — the part that is always missing when somebody asks a year later.