I had a very complex piece of logic, with many many many moving parts. So I implemented many paths of that logic by hand, every one with their own specifics. Every path took something like 200-400 lines of code.

When this was done and correct. It was difficult to see the moving parts through the forest. Some code was similar but still a bit different, and hard to think about and spread in many places.

I put everything into an Llm and asked about isolation, architecture and refactoring.

And it actually gave me pretty good abstractions and a good architecture. It didn't include every possible path, but was easy enough to be continued by hand.

It's not that I would not have tought about it. But it was easier that way, and probably my handcrafted solution would be very similar (+headache).

Of course, I reviewed it extensively, and reimplemented every missing path and corrected the ones that were buggy now by hand.

For the experiment, I played with agents to fill the missing parts, it was a disaster :)