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 b

Answer 1

Because, only by knowing the rule, will you know when to break it.

Using browser-specific extensions isn't bad, but it is something you want to do on purpose, not blindly.

Validation points out the places where you deviate from the standard. Maybe you needed to, maybe you didn't, that decision is yours.