What's the point of valid CSS/HTML?

Question

If I've tested my pages in most major browsers, why would I need to maintain a validated code? I want to use box-shadows and corner radius if they're supported in WebKit browsers and Firefox. I don't care if they don't show up on Internet Explorer. But I keep my HTTP requests down by not including images instead.

Are there are advantages to valid code? In SEO or otherwise?

Answer 1

• Google prefers it so it is good for SEO.
• It makes your web page more likely to work in browsers you haven't tested.
• It allows you to generate or use your page as an XML document.
• It makes you look more professional (to some developers at least)
• Compliant browsers can render XHTML faster than HTML in quirks mode.
• It points out a bunch of obscure bugs you've probably missed that affect things you probably haven't tested e.g. the codepage or language set of the page.