The deliverable people value most and receive least.
WHAT TO DOCUMENT
How to deploy How to run the project locally Environment variables required, and what each does
Where things live: code, uploads, configuration, logs
Scheduled tasks and what they do Third-party services and integrations Known issues and workarounds How to restore from backup
WHERE TO KEEP IT
In the repository, so it lives with the code and changes with it.
A README covering setup and deployment is the minimum.
WHAT MAKES IT USEFUL
Written for someone who has never seen the project Specific commands rather than descriptions of what to do Kept current, because documentation describing a setup from two years ago misleads
THE TEST
Could a competent developer who has never seen this project get it running locally and deploy it, using only the documentation?
If not, it is incomplete.
WHY IT MATTERS COMMERCIALLY
A project nobody else can maintain is a liability to the client and a constraint on you. Good documentation is what lets you hand work over and move on.
