Most of my old defects fall into tradeoffs I knowingly made at the time: well, this edge case is really unlikely, not worth pursuing a fix, the remediation won't be bad, some jank isn't going to annoy users too much, etc. But LLMs don't care: a bug is a bug, and they'll happily surface it for you.

Being able to take an old code base up to 100% test coverage alone is incredibly eye opening.