When we reach for it
Knowledge that changes, is private, or must be attributable — support material, policies, contracts, internal documentation. Citations are why this is the default for the work: an answer a reader can open and check is a different product from an answer they are asked to trust.
When we would argue against it
Small, stable corpora. If the whole body of knowledge fits in a prompt, a retrieval layer is machinery earning nothing. And where the documents contradict one another, retrieval surfaces the contradiction rather than resolving it — a content problem wearing a technical costume.
What it looks like in delivery
Chunking and retrieval evaluated separately from generation, because most bad answers are retrieval failures wearing a model’s voice. Retrieval is scored against a query set drawn from what people actually asked, and “I do not have that” is a designed answer rather than a failure.