Depending on the complexity of your code, you may even want to test it with different browsers to make sure that your site looks the same in all of them, since it's possible that you are using features of HTML and CSS that are only implemented in some browsers but not others.
Others validate only when they make a major design change.
I always validate the template for my pages when I make a major design change.
Syntactically, the sentence is correct, since all the elements of the sentence, subject ("Chris"), verb ("ate") and object ("a pie") are in the right order.
Semantically, however, the sentence describes a different thing from what you meant.
Validating your web page does not ensure that it will appear the way you want it to.