When I look back over my career to date there are so many examples of nightmare degraded codebases that I would love to have hit with a bunch of coding agents.
I remember the pain of upgrading a poorly-tested codebase from Python 2 to Python 3 - months of work that only happened because one brave engineer pulled a skunkworks project on it.
One of my favorite things about working with coding agents is that my tolerance for poorly tested, badly structured code has gone way down. I used to have to take on technical debt because I couldn't schedule the time to pay it down. Now I can use agents to eliminate that almost as soon as I spot it.