A common SEO tip for web developers is to keep your content to markup ratio high.  This is supposed to make the crawling of your site easier, more efficient, and faster.  It is possible, however, that more modern site crawlers like Google ignore code already, since they behave like a text based browser anyway.  However, implementing this as a SEO strategy cannot hurt. In fact, it has benefits for not only SEO reasons, but for general web development practices as well:

• Keeping the amount of code on the page low helps overall site maintenance and usability, focusing on your content. 
• Including CSS and JavaScript in external files increase content-to-code ratio as well as making your site easier to maintain. 
• Having validated HTML code will help the crawlers understand your site , as well as make your code compliant for maximum browser readability and performance.

For more information:

• Phoenix Realm – Why Clean Markup Matters To Your SEO 
• All Your Web – HTML to test Ratio
• SEO Workers – Isn’t the Code to Text Ratio Important for SEO?