This doesn’t matter in the age of AI - when you get a new requirement just tell the AI to fulfill it and the old requirements (perhaps backed by a decent test suite?) and let it figure out the details, up to and including totally trashing the old implementation and creating an entirely new one from scratch that matches all the requirements.
For performance, give the AI a benchmark and let it figure it out as well. You can create teams of agents each coming up with an implementation and killing the ones that don’t make the cut.
Or so goes the gospel in the age of AI. I’m being totally sarcastic, I don’t believe in AI coding