What do we get from implementing RDF and linked data to our Websites?

I have been implementing for some time different things to my Website.

I am currently trying to figure out what value can we get from the Web we know today while implementing linked data and semantics to our Websites.

There are HTML5, WAI-ARIA, RDF, OWL, FOAF, SKOS, SKOC, SIOC .... - any value of implementing them today?

Maybe SEO and Google Search question, but is there someone who can give approximative answer?

Any ideas? Hopes? Information about that?

Thank You very much for help and shared links!