The WebKit team has an interesting policy that I think we should apply more aggressively to most software we write. It turns out, they don't tolerate any performance regressions, at all.
We have a zero-tolerance policy for performance regressions. If a patch lands that regresses performance according to our benchmarks, then the person responsible must either back the patch out of the tree or drop everything immediately and fix the regression.
Right below this longer quote, you can see in large text:
Performance is a top priority for WebKit. We adhere to a simple directive for all work we do on WebKit: The way to make a program faster is to never let it get slower.
I think this is something we don’t pay as much attention to.
Yes, our machines get faster every now and then — but that doesn’t mean that we should make our apps slower… It’s a balancing act, of course.
It’s also a good policy to add a test if you found a bug in the app that wasn’t covered by a test already.