It's mainly an advanced coordination book. It starts pretty slow although it isn't beginner's stuff, and some of the combinations are pretty challenging.
One of the main points is to develop ambidexterity. Also the author, Gary Chester, was an advocate of singing the different parts as you play them, in order to better internalize. I would say one of the challenges is to make the exercises sound musical...
Published at the start of the 80s, if I can remember well, the book became more famous when Dave Weckl stated having been studying with Gary Chester.
Cheers
Alain