From that I know whether or not I have any interest in reading the book.
During a fall 2007 writing conference in Lincoln, Neb., author Stephanie Bond encouraged aspiring authors to start planning their books by writing the synopsis that would appear on the published books back cover or inside flap.
This is a fun way to get your creative juices going and to think about the direction you want the story to take.
Here is an example I came up with for a book I have no plans to write about:
Layla Crawford was trouble and she knew it. Whether she is in the board room at her New York City ad agency or in a crowded night club, men and women alike have grown to fear, admire and envy Layla for her ability to command a situation.
It all disappears when the president of her company flees the country to evade tax fraud and sets Layla up to take the fall. Facing possible jail time and wrongfully accused, she must turn to the smooth-talking Donovan Ayers. The top white-collar criminal defense attorney has butted heads with Layla in the past, but she knows he is her only hope to return her life to solid ground.
Layla and Donovan must fight the clock - and their change in feelings toward one another - to find the answers to all the puzzles that keep appearing. In their quest for justice they find more sinister deals then they imagined possible, and they also learn that love might have a place in their lives after all.
By writing this blurb, I could now surmise many things about the potential plot for the book. I know it will have a romantic and adventurous feel to it. I also know that I will be taking my character from a high to a low.
While this alone would not work to plan a full book, it does get your mind going and help you build your own excitement for your book.