The main advantages that derive from having valid HTML & XTML.

• Validation exposes errors in your programming and potential vulnerabilities in your code.
• People with disabilities will be able to access your page and the overall experience for the end user will be improved.
• Validation helps you reduce the amount of coding on your pages.
• Your website can be easily accessed via different devices – PCs, laptops, PDAs, Blackberry, mobile phones and so on.
• Validation means your website is fully compatible with a wide range of dynamic pages.
• All current and future browsers will display pages in the same way, or at least in a very similar fashion.
• Having a correct validation will help the spider easily read your site with no interruption.

The validation of your HTML or CSS code has certain benefits. It protects your pages from problems which arise from syntax errors in your code due to the different ways which search engines and other browsers interpret it. If you get into the habit of validating your web pages, your website will load faster, be more search engine friendly and accessible to a greater range of devices and therefore appeal to a larger share of internet traffic.