1. The Future of web design
The first reason why you should start using Html5 today is that Html5 and Css3 are the future of web design& development, and takes ful advantage of the code's design capabilities. With Html5 you will write cleaner code and will get all of the other benefits and fun features of modern and evolved web design. Markups are really simplified and more semantic, and your code will be flushing over the multitude of existing devices in the market today.
2. Mobile compatibility
Mobile devices are taking over the world, which means that more and more users will be using their mobile browsers to view your website or applications. Html5 is the most functional tool for developing mobile sites and apps, beacause mobile browsers have fully adopted Html5 as the structure of the web pages, as a consequence of the massive development represented byresponsive web design. Some new Html5 meta tags are fundamental (eg. viewport) for configuring measures and settings on the various browsers resolutions and settings.
3. Cross Browser Support
4. Games Development
HTML5 provides a great mobile friendly way to develop interactive games. If you’ve built Flash games before, you’ll love building games with Html5.
5. Interactive applications
Html5 tags allow you to produce more interactive and animated objects than the previous rich internet application platforms like Flash! Html5 also comes with a lot of great APIs that allow developers to build a better user experience.
6. Better Storage System
Local clients/users storage is great for many reasons and it's one of the Html5 tools that are making web apps possible without third party plugins. Being able to store data in the user's browser allows you to easily create such app features like: storing user information, the ability to cache data, the ability to load the user's previous application's status and more.
7. Cleaner Code
With the new Html 5 tags like:
developers are able to code their markup more cleanly as well as keep their CSS3 better organized. If you are a fan of simple, elegant, easy to read code then Html5 is the right solution for you.
8. Doctype definitions
The simplicity of the Doctype is one of the most important features of Html5 that web developers will notice immediately. No more long unreadable lines of code and no more dirty head tags filled with doctype attributes.
9. Video and Audio Support
Forget Flash Player and other and other media players, make your videos and audio fully accessible with the new HTML5 video and audio tags. The huge list of parameters of the new media tags allow programmers to get the app visible and working correctly in the whole device/browsers options existant actually.
The new Html5 headings tags allow screen readers to easily access content. With new semantic tags screen readers can better examine the Html document and enjoy a better experience.