If you are doing any sort of business online, or selling something ,a product or anything else, your services, affiliate offers, etc. after the years of testing different layouts, this narrow main content pane has consistently preformed the best and yet very few theme developers use this layout when designing free or premium wordpress themes. While you should always be testing things like graphics, font size, colors, and the like JohnGalt will help take a big part of guesswork out of the equation by providing a layout proven to convert.