Documentation communicates intent, design decisions, and usage patterns that are often implicit or scattered throughout the source code, making it valuable even when the code is available.

Code is the final implementation, you / an AI can read the code and explain what it does, but it can't explain why it was written or when it should be used without more context.

Docs function both as a summary of code (functionality) and use cases. The day ai can infer both from code perfectly is the day ai can write the dependency on the fly.