As not all codebases are well-written, I have found useful once to get an LLM to produce code that does X, essentially distilling from a codebase that does XYZ. I found that reviewing the code the LLM producced, after feeding the original codebase in the context, was easier than going through the (not very well-written) codebase myself. Of course this was just the starting point, there was a ton of things the LLM "misunderstood", and then there was a ton of manual work, but it is an (admittedly rarer) example for me where "AI-generated" code is easier to read than code written by (those) humans, and it was actually useful having that at that point.