There are many types of structured data types within the Google Developer page. Among them: Article, Book, Breadcrumb, and Carousel, to name a few.
But more structured data types exist in places like Schema.org that don’t exist within Google’s own developer page.
All of the content on Google’s developer page is eligible for rich results, but the same is not true of the structured data types from Schema.org. So, is there any SEO value in adding these extra structured data?
This is precisely the question that was asked to Google’s John Mueller in a Webmaster Hangout session.
According to Mueller, although the structured data from Schema.org that’s not documented on Google’s own developer page provide no rich results, there can still be benefits.
Specifically, extra structured data can further help Google understand the contents and context of a webpage.
However, Mueller warns to pay attention to how much of this extra structured data is added to a webpage.
He says in the Webmaster Hangout, “… it’s also something where it’s very easy to go overboard because there are just so many different things you can mark up with Schema.org.”
And although this additional structured data poses no harm to the website, Mueller adds that, “… you can spend a lot of time marking up all of those individual elements and there’s absolutely zero effect on your search results, even if we were to process that.”
So, the question has been answered: Extra structured data that comes from sources outside of Google’s own developer’s page can still provide value, just not to the point where it should be the main priority. Remember: those structured data types can’t enhance your SERP listing.