HTML headings serve two purposes for non-sighted users:
- They provide an outline of the page, so users can understand how the page is structured, and how all the sections relate to one another.
- They provide a target so users can jump from heading to heading with a single keystroke (e.g., the letter “H” in some screen readers)
With the first purpose in mind, headings should be used in proper order whenever possible. That is, you shouldn’t have H2 headings with no parent H1 heading, and all headings should be in order with no heading levels skipped.
Additional information is available on the WebFirst, The Importance of Headings and How to Use Them.