They frustrate and drive away customers, failing to generate revenues. Worse, they're vulnerable to hackers and bandits. Security begins even before you take your site live. Complex sites also need to undergo extensive beta-testing for security. It's equally important to keep your content fresh, so change it frequently.
Stale content undermines the best page design.
Customers bored by your site will stop coming back. Outdated content also makes you look unprofessional and cavalier about the people you depend on for business. You should also check links to other Web pages and update the ones that moved or are no longer relevant. If you have a message board or a guest book, remove old data so your site looks current. And finally, study your site's traffic statistics to learn how many hits it's receiving, what pages are the most popular, and what time your site is the busiest.