This has been saving me a lot of time as well in a decade old code base. I can paste a stack trace and provide additional relevant context, then ask the LLM to do a first pass debug.

From that I usually get a list of file+lines to manually review, along with some initial leads to chase.

Another use case is when fixing performance issues. I can feature flag my fix and ask the model to confirm the new code path will produce the same result for a given set of inputs. We also have test coverage for this kind of thing, but the LLM can do a once-over and point out some flaws before I ever run those tests.

I haven’t gotten to the point where it writes much code for me beyond the auto-complete, which has been a modest boost in efficiency.