Currently the latest version is HTMS5. It has a design of defining all elements individually. Such as, paragraph, header, footer etc etc. Hence, using semantic HTML, you can guide crawlers specifically to list certain parts of website and define it accordingly. It helps SEO in a manner that a crawler can identify particular sections of website and can crawl it according to its importance.

It is mostly used for ranking certain topics of a single page, on a similar note of a blog page. It can also be used if you want to get rankings for particular blog post from a single page, you should use semantic HTML to get your purpose solved.

Hope this helps!