Here's a situation for you: you're at dinner with your parents, or your partner, or your partner's parents, or your partner's friends. They hear that you study or make games for a living, or that games are the primary way that you spend your leisure time. They tell you that their 8-year old nephew would love to hang out with you, because you love doing the same "childish" activity that they do. Or they want to know why you'd spend so much time and mental energy engaging with a violent, masculinist, repetitive, and stupid bunch of artifacts.
Most of these people, they play FarmVille or Solitaire or Tetris or Snood to fill their time. At family gatherings, they're the first to drag out the Scrabble or Monopoly board. They don't quite recognize that games and videogames are already important to them, too.
Instead of getting flustered, now you've got a book to hand them (or, at the very least, you'll have a handy mental volume of examples and arguments to draw from). It will show them that there are games in between what they play and what "gamers" play, games that do things and explore all sorts of terrain that they didn't even know the medium could. Finally, it articulates a future for games and the people who play them that even you (as a gamer, developer, or scholar) probably haven't thought of before.