The importance and compared merits of heading tag in website pages and posts has been (and still is) generously commented and there seems to be little argument about it: heading tags are necessary to boost SEO and improve user experience.
HEADING IS CODE NAME FOR STRUCTURE
Heading tags (or title tags) are designed to add two elements to content: hierarchy and rhythm, and one major component to search engine parsing: identity.
Imagine a block of text on any topic that would be presented in form of a big clump, possibly with paragraphs, but without visual effects to outline its essence.
The result is a rather uninviting, uninteresting and inefficient post. Very few would be intrigued enough to read it. There is no clear display of what it is all about, the question it raises or the answer it provides.
The purpose of heading tags from a strictly redactional point of view is to be visually enticing and deliver a sort of summary of the content itself. In other words, they constitute the skeleton of web content from the spine (main heading) to limbs (subheadings) to fingers and toes (lower subheadings).
HEADING TAGS RESPECT THE CHAIN OF COMMAND
Typically, the hierarchy in headers is