It will help to keep users coming back:
Suppose you walk down your local hight streeet and notice that a shop there never changes its front window - the products are always the same - what do you feel? You may not bother looking in again, since you know it's going to be the same.
It's the same with your website - you need to tell potential clients about the latest news, products and offers to get their interest and show that something is hapenning!
(Image courtesy of Serge Bertasius Photography at FreeDigitalPhotos.net)