Getting good search results is the goal of every business website. High quality information always gets results. However, if search engines can't understand a web page, they will not give it the ranking it deserves. A good web page is valid, so a good search engine optimizer will ensure that all your pages validate. If you simply want beautiful web pages that only your friends can find, don't worry about validation.
If you need a successful web site, make sure it's valid, accessible and provides all the information customers want. That's how a web site finds new customers and becomes profitable.