This book will definately help with planning - a must have, especially for trainee teachers.
It's really easy to read so you don't find yourself switiching off. It's not a book you should read cover-to-cover (if you should ever have the time to!), instead, read the section relevant to what you're about to teach. It gives you a good idea of the errors that may come up and why.
The book gives examples of misconceptions and this is useful to see if the kids really understand what they are doing. I sometimes put these examples on the board and ask the kids to mark them - this is useful for them to understand where they're going wrong or could go wrong.
Also, it shows you the progression, linked to the NNS so you can see where they came from and where they should be moving to.
This, along with Shirley Clarke books, are definately the best books that I bought during my teacher training - money well spent.
If you're not a trainee or an NQT this is still v. useful to have on your shelf - if only to dip into everytime you teach a new unit.