For sites that deal with products or time sensitive information, it’s a great idea to go back and edit older posts to reflect new information.
For example, you may post when a product is announced and again when it ships. Search engine visitors might come to your first post in droves (perhaps it was linked to quite a bit), even after the product has shipped. Adding a small note that the product is now shipping, along with a link to your newest post is a great way to both increase page views and increase the satisfaction of your visitors.
Real life example – Samsung P207