As the web evolves and expands it is important for the technologies associated with the web to grow along with it. First, it is important to have “clean markup.” Essentially this means free of clutter, standards- compliant, and the correct usage of tags and structures of each language for their intended purpose. Basically it leaves each document structured and organized thereby making the entire processes streamlined and easy to understand. Standards compliant means that the pages you’ve designed validate with the standards laid out by the W3C for html, css, and xml.
Some may if it works what’s the point of making it streamlined and easy to understand? Other than the very obvious answer that it’s clearly simpler, it will also aid yourself or anyone else that is tasked with updating the site in the future. Just do it right the first time, a good motto to live by.
Also clean markup and compliance with all standards will go a long way in ensuring your site will work across mobile devices, and will translate into numerous languages.
The entirety of this article was in my opinion common sense. Basically do it right the first time and keep it simple so you don’t screw yourself over if something doesn’t work properly.