The heading levels (1-6) are often considered a way of describing and determining the “importance” of a heading, with h1
being the most important. This might be reflected in the visual appearance of headings—higher-level headings typically appear as bigger and bolder text than lower-level headings.
But you can't just put an “important” heading anywhere. Its heading level relates to how much content it refers to, and that has to do with structure.
Reflecting structure accurately allows screen-reader users to use their screen reader's heading-navigation feature to navigate by heading level, building up an idea of document structure. It also ensures that, for people who use custom stylesheets, heading structure is preserved even when the appearance of headings is changed.... Read more about ✎ Technique: Heading structure