Most of this book is pretty useful, worth having if you are a Mage player or Storyteller but its the last nine pages that make it truly essential to the game. The Page for each Sphere descriptions of just what you can and cannot do with each level of power in each sphere of Magic was a godsend in the early days of mage and even now with 2nd and revised editions, this little book is great to have to hand both for players and ST's alike.