Counterpoint: Why should my println debugging get committed? They're not "important" for the final product but important for development.
I am a black kettle here as I frequently commit individual lines amongst a sea of changes, but I do appreciate the theoretical stance of jj.
(though for debug printfs in particular, the Right Thing is proper logging with log levels, but I myself love printf debugging and so sometimes don't do that either. Which is why carrying local patches is nice.)
It's really important to catch bugs early, because it's a lot more expensive to fix them later -- even if only as late as in CI before merging.