It's important to include many different channels of advertising media because each channel reaches a different audience.  When people see your product in a direct mail piece, and later sees your website and printed ad, your company gains credibility. Greater credibility will lead to greater sales. Most people need to see a sales message more than once before acting on it.  And different types of people buy things differently.  Some like to order from catalogues, others like to search the internet, while others order from TV commercials.  

They say, "To achieve your company's maximum potential, it is no longer enough to be good at just one type of marketing.  Yes, you need to continue to do what you are already doing. But you must also expand into several additional channels, especially on the Internet.  When you do you will see how it all works together, giving a boost to every effort to reach your buyers."