It's the first day of the new year. You have your brand new wardrobe at your disposal. You don your brand new shirt and suit. Put on a smashing pair black shoes and head out the door. Now let's say that you never returned home for a year. Sounds ridiculous. But keep with me. Your clothes would look great for a week or two. But would be walking off you after a month. Those brand new shoes would have seen better days. All in all you would look tired and unloved.
And the same goes for marketing messages - especially on a website. Keeping the same message, images and information on a website for longer than a few weeks, could mean that your message becomes lost - or never looked at - or somewhat bedraggled! Keep content fresh, keep your ideas flowing and above all - keep people coming back to your website.