For most companies, knowledge *usually* isn't enough. So...even if you're the best WHH (white hat hacker) in the world, there are some/all/one companies/company that will not hire you because you don't have a slip of paper saying that you can perfom the tasks of a security consultant.

My advice...if you already have the knowledge, then passing a course or getting a certification would be no hard work anyways, right?

Get your certifications cause it'll pay off in the long run!