Quality of code

Not  all code are created equal. Some pieces of code are more important than others. The code that powers critical parts of a nuclear power plant is hopefully of a much higher standard than the code behind this site, but how do you recognize which quality of code you should aim for when developing websites?

A website may not have one set level for all content - usually the various pieces which make up the site (no matter if it be classes, files or functions - in PHP). On the level you’re looking, let me suggest, for each piece you judge the required (minimum) quality on two simple parameters:

Business/Real world value: What’s the consequence if the code breaks? are you loosing money? or is it “just” an embarrassment”? The higher the stakes the more effort should be put into the code.

Scope of impact: How large a part of your website breaks if the code fails.

While you may not have a precise scientific way of measuring the two, I’m quite certain, that most developers have a pretty good gut feeling on both, and ought to be able to set a suitable quality level using just that.

Is it so or are there better ways to find acceptable quality levels?