It's a mix. There are some projects where I let the LLM mostly run free and I focus on architecture. Even through some scary parts. Recently I picked a parallelization scheme for this and let the LLM cook. I have no idea how it implemented it, except that it (supposedly) "does it the way I asked:

https://github.com/ityonemo/bpa

For my projects that I use day to day in prod there is considerably more hand-holding and code review.