Displaying special content like banners, videos, special messages, instructions, etc is a very powerful capability of your site to maximize your ability to inform your customers and hopefully capture more sales.
Maybe you offer free items when customers purchase products from a certain manufacturer. Now you can display a message saying that on the Product Details page for any product that is made by that manufacturer. Best of all, you don't have to do it for every product. Using the Generic Variable Merges, you can accomplish this on one page with only a little bit of code.