Why does the Open Graph specification requires, as opposed to merely support, suggest or recommend, the use of og:title when in many cases it will be fully redundant with <title></title> from HTML, RDFa's superset?
What happens if, in the interests of brevity, normalisation, and a general dislike of bureaucratic duplication, one chooses to omit og:title?
The title element and the og:title property typically don’t have the same content.
Both typically give the title of the main entity, but the title element should provide context (e.g., the site name) in addition.
(But even if they would have the same content, it might be preferable to allow consumers getting all OGP data by parsing just the RDFa, not also the HTML.)
<title>opengraph - In a website, what is the value of og:title as opposed to a plain title element? - Stack Overflow</title>
<meta name="twitter:title" property="og:title" itemprop="title name" content="In a website, what is the value of og:title as opposed to a plain title element?" />
The title is:
opengraph - In a website, what is the value of og:title as opposed to a plain title element? - Stack Overflow
The og:title is:
In a website, what is the value of og:title as opposed to a plain title element?
Then you could provide the og:title property on the title element:
<title property="og:title">…</title>
(But note that some OGP consumers might, unfortunately, not support anything else than meta elements.)