You might have seen elaborate documentation that repeats code, looks at the same API multiple times with many examples and case studies. Context is key: who wrote it, for whom, and what material it is covering, and what resources did they have.

Fundamental library code often has Elaborate documentation, for example, the standard library, highly reusable frameworks like serde and tokio. Teams responsible for this code often have appropriate resources to write and maintain elaborate documentation.

Library code is often stable, so the community is going to extract a significant benefit from elaborate documentation before it needs to be reworked.

Application code has the opposite traits: it has few users, solves a specific problem, and changes often. For application code elaborate documentation quickly becomes outdated and misleading. It is also difficult to extract a positive RoI from boilerplate docs even while they are up to date, because there are only a few users.