Semantic HTML5 elements are necessary for accessibility and machine-parsing of your content, which increases findability. What this means pragmatically: Scree

Semantic HTML5 elements are necessary for accessibility and machine-parsing of your content, which increases findability. What this means pragmatically: Screen readers will be able to more intelligently interact with a website. Navigation, for example, could only be read out loud when the user requests it instead of every time a page loads. Search engines, when parsing your page, will be able to more easily get a general idea of what the page is about. Right now we can only tell headers, paragraphs, and lists; with HTML5 parsers will be able to not only determine the former, but also which content is more important. The more semantic the markup, the more a machine-parser can figure out about the meaning behind a page. It's the same argument as a mass of divs and spans (or tables!) versus h1s, paragraphs, and dls. Ultimately, not only does it add context to your content, but it makes it easier and more concise to produce the markup: you don't need <div class="aside"></div> anymore - you just need <aside></aside>.