Small add: "generally competent engineers" can sometimes (almost) inline most of the code completeness details for cheap, reducing their cost greatly.
Writing documentation is always a time sink, though, in my experience. Or maybe I'm just not good at it :P It's usually an additional day of work overall, though.
For end-user products with a user interface, less so as it comes down to being flexible... similar with dashboards, as a developer I often don't know what is wanted up front... when something is asked for and you learn the domain more, it can come together easier. Larger projects with a front end component and many developers, nearly have to forget it at the dev level.
And it saves you days and days of re-discovering truths about your code weeks/months/years down the line. Sometimes those rediscovered facts are not even true which will come bite you big time.
Integrate your documentation with your testing. That makes it easier to create and maintain. You don't have comprehensive automatic tests? Then that's your problem right there.
* comments in code
* team-based comments
* project design docs
* knowledge-base articles for handling on-call rotation around feature
* how-to guides for customers
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.