I think more specifically, if you don't have strong guidance to the LLM on how a project is organized and where things should go, things go pretty far off the rails.

I tried to have an LLM fully write a Python library for me. I wrote an extensive, detailed requirements doc, and it looked close enough that I accepted the code. But as I read through it more closely, I realized it was duplicating code in confusing ways, and overall it took longer than just getting the bones down myself, first.

Some coding agents are now more actively indexing code, I think that should help with this problem