Honestly, this more of a question about scope of the application and the potential threat vectors.
If the GP is creating software that will never leave their machine(s) and is for personal usage only, I'd argue the code quality likely doesn't matter. If it's some enterprise production software that hundreds to millions of users depend on, software that manages sensitive data, etc., then I would argue code quality should asymptotically approach perfection.
However, I have many moons of programming under my belt. I would honestly say that I am not sure what good code even is. Good to who? Good for what? Good how?
I truly believe that most competent developers (however one defines competent) would be utterly appalled at the quality of the human-written code on some of the services they frequently use.
I apply the Herbie Hancock philosophy when defining good code. When once asked what is Jazz music, Herbie responded with, "I can't describe it in words, but I know it when I hear it."