There's a lot of people here that clearly haven't ever tried what you're describing op (or maybe tried recent AI at all).

I have. I think it's a totally valid question. Sometimes when I'm getting AI to do stuff it reads the docs and then tries stuff anyway and finds the docs are wrong.

I also often use AI to generate docs for undocumented things.

But I think it does still make sense to have docs for a few reasons:

1. They show the intent explicitly, rather than having it inferred. Same reason anything explicit is better than implicit, e.g. static types.
2. It spends fewer tokens to read docs than to constantly reverse engineer software.
3. It's also quicker.
4. Sometimes you do still want to understand the thing...