Schema.org provides you a good way to optimize your website for search engines. SEO surely means much more than that, but the usage of Schema.org will improve your visibility to Google & Co. a lot. Have you ever, for example, checked out movie search results at a website like IMDB.com or Wikipedia.org? They will mostly show you additional information for that particular movie, such as a trailer link, a link to release dates, maybe user ratings for this movie (check out the tiny yellow stars there!) and sometimes information about the actors, the director and much more, depending on your search query – and the website’s markup with Schema.org. So Google is not that intelligent that they know what the website is about – you gotta ensure this yourself by adding Schema.org microdata. While it does not directly improve your website’s rankings, the search results for your page will certainly look more appealing to users since additional information will be included.