I made the decision to have only 1 H1 tag because of SEO concerns, but also because of the accessibility. You also had to see, that in the most important place – single article post – title gets H1, it’s on line 32.
By using <h1>s for each section, you are semantically stating to
screen reader users that the sub-sections are equal to and parallel to
the document title. This is just not correct. Now if the outlining
mechanisms worked, the browser would appropriately present the section
H1s as second level headings. But it doesn’t work. There is no
difference in how a heading structure would be presented in an
HTML4/XHTML document headings and in an HTML5 document with sectioning
elements (excepting that one version of JAWS that tried and failed
miserably to implement the outlining mechanism). So at present, using
<h1>s everywhere results in an incorrect document structure as
presented to screen reader users regardless of the flavor of HMTL
used.
You asked how this impacts users…
It is a common strategy for screen reader users to quickly navigate to
the first <h1> in a document (typically by pressing the 1 key) to
quickly determine the document title. This almost always places focus
directly at the beginning of the main content area. They can also then
navigate the <h2>s in a document (typically by pressing the 2 key),
etc. to determine the major page sections and sub-sections.
Additionally, the user can open a list of the headings and can
navigate/filter those headings by level.
If H1s are used to begin each sub-section, this functionality becomes
much more difficult as they cannot differentiate document and section
headings (and potentially sub-section and sub-sub section). The
ability to quickly jump to the document title and beginning of the
main content is diminished. How can they know which of all the <h1>s
is the document title and which are section headings if they are
presented identically?
This can also impact users that use keyboard enhancement extensions or
voice control to navigate by headings. They would expect that headings
that appear smaller and below larger headings to be sub-headings, when
in your presented structure they would be parallel headings.
https://webaim.org/discussion/mail_thread?thread=6343
