There are cases where I would start the coding process by copy-pasting existing code (e.g. test suites, new screens in the UI) and this is where LLMs work especially well and produce code that is majority of the time production-ready as-is.

A common prompt I use is approximately ”Write tests for file X, look at Y on how to setup mocks.”

This is probably not ”de novo” and in terms of writing is maybe closer to something like updating a case study powerpoint with the current customer’s data.