Web standards, established by the World Wide Web Consortium (W3C), determine the best coding practices for HTML, CSS, and other web technology. This is intended to ensure that browsers view websites the way they were intended and browser developers have a base for which to develop their rendering engines.
Whether your dedicated server runs one web site or one hundred, you will invariably have to deal with browser compatibility and possibly even accessibility issues. Web standards can help you along the way. Moreover, poorly coded websites usually take more bandwidth and may even be less secure than sites with clean, concise code. Less bandwidth means that sites load faster, and cost less. Sites with correctly-written code are less susceptible to vulnerabilities. And websites written according to standards perform better in search engine rankings.
Accessibility is another issue that can affect your server both financially and technically. All web users deserve access to your site, and web accessibility standards can help you achieve that. For a business this will give you more customers and also help you avoid possible legal disputes in the future.
Most importantly of all, you want your websites to reach as many people as possible and deliver your message or business without complications. By writing your code to standards first, you ensure you at least will reach those browsers which are standards-compliant. You can then go back and adjust it to work with those that are not.