Actually World Wide Web Consortium (W3C) is not designed for Search Engine Optimization(SEO) Purpose, but if we follow W3C Standard website can get good place in Search Engine. I have list out some reason here :
1. There is less chance to wrong in HTML tag style when we follow W3C standard.2. Less use of javascript3. Title in hyperlinks, helps to increase more words for robot.4. In W3C standard we must need to define tag name in image so crawller can read it and can get position in Image search