Presumably all the structure and section headings that they recommend don't have to be rendered by a browser as visible to humans. The LLMs should be smart enough to understand HTML directives that don't add a lot of unnecessary visual structure.
They don't have to be rendered in the browser, but having all of the structures and section headings help humans to, so I would recommend it. :)
It can go too far. Too many section headings and it becomes unreadable, like an undergraduate textbook where you're constantly being distracted by sections and boxes.