* comments in code
* team-based comments
* project design docs
* knowledge-base articles for handling on-call rotation around feature
* how-to guides for customers
Each of these has a different cost and a different direct/external usefulness. I absolutely believe in good documentation and I absolutely believe that it's valuable. It does not negate the extra cost of including these forms of documentation - especially the "not-in-code" documentation.
Of course they "cost". But the issue is the mindset that they are "extra". They are not. They are an integral part to professional software engineering. You can't take them away without moving from a professional craft into some hobby hack.
When developing medicine you wouldn't consider safety studies as "extra". When you fly an airplane then the take off checklist is not "extra". Arguing that automated test suites or documentation are just "extra" on top of making software and could be skipped is similar to arguing that you could fly a plane without any checklists or releasing medicine to the public without evaluating its safety. That's just unprofessional nonsense.
