A website is a real-time marketing tool. Out of date information, broken links and stale content are just some of the areas that may mean your website is in need of further development. For example, stagnant content could get your site demoted by the leading search engines.
Even if on the surface your website looks OK, it may be suffering from technical issues behind the scenes. Poorly optimised graphics, inefficient coding, overuse of graphical gimmicks, poor navigation - the list goes on.