||The key to strong interior design in books is making the text easy-to-ready. On books other than those that are composed of straight type, such as fiction, this is done by breaking up the text out of straight type as much as possible.
We do this by making judicious use of short paragraphs, subheadings, graphics (such as charts, illustrations and photos), screens, and by altering type (bolds, italics, etc.). All these factors improve the readablity, feel, and organization of a book. And thus, they increase sales.
In how-to and artistic books, where creative use of white space brings out the best in a book, readers have more difficulty navigating through straight running type such as would be found in fiction, and thus interior design takes on more sales importance.(In fiction and non-fiction books, we still want a nice design, but other than doing a good job with type, there are few design decisiopns. These books are pretty much straight text.)