On a long web page that is mainly text, frequent sub-headlines are desirable. Make sure at least one headline is visible on the screen. That's approximately one headline for every 100-200 words.
As people scroll down a text page, the main page headline disappears from sight. The words lose all context. Without sub-headlines, people can feel anxious—and quit the page without even trying to read that great grey wall of words.
Therefore, subdivide long pages into smaller chunks of information, each with its own topic and sub-headline. A chunk might be just one paragraph—or several paragraphs.
Clear, complete sub-headlines have at least four keywords and summarize the next chunk of content. Vague headings or questions don't work well.
Good headlines and sub-headlines can collectively summarize the entire web page. That's great for skim-readers (i.e. everyone).