On government projects the document is the deliverable

Consulting on a ministry system taught me that the artefact with the longest half-life is not the service — it is the specification everyone signed.

What earns its place

• Interfaces, with the failure modes named.
• Security controls mapped to the requirement that demanded them.
• A sequencing plan, so "phase two" means something.

What does not: diagrams that restate the text, and any section that exists so the table of contents looks thorough.

The test I use now — if a paragraph could not settle a disagreement six months later, it is decoration.