In my experience it works well when you discuss specifics and compare approaches - how do I do $x, compare $y and $z, I have this functionality so far, help me

In my experience it works well when you discuss specifics and compare approaches - how do I do $x, compare $y and $z, I have this functionality so far, help me extend it in such and such way etc. I don't think that asking it for a big refactor, or generally leaving it do all the coding on its own is the way to go. A lot of the value it provides comes from the conversation you're having with it and from the fact that it can help you discover patterns and tools you didn't know existed (e.g. what are the best practices for solving a given problem). Using the paid version with GPT-4 is much better too.