I'm a casual player and don't study or practice ever. But I'm just interested enough to consider reading a book on chess from time to time. The Shredder app I have on my phone pegs me at 1450 Elo rating, and I'm probably at the bottom range of what level player might find this book useful.
I enjoyed the format where Silman annotates games against his students, including their thoughts on why moves were made, and his notes on these thoughts. A majority of the content relates to the middle game, and so there isn't too much strict theory on what is the correct move.
One of my weaknesses is having gotten through an opening in fair shape, how to best proceed with figuring out and acting on a plan for what should come next. This book gives a nice framework to use for analyzing the basic aspects of a position which focuses on listing the imbalances (in material, development, space, pawn structure, etc.) which are all simple enough that I can at least grasp the basics. Once you have a handle on where each side stands in relation to these imbalances, you have a fighting chance at figuring out how to capitalize on your strengths and attack the other side's weaknesses. You also come away with a better sense of when/what pieces it makes sense for you to exchange through the middle game.
It's all written in clear English and like most self-study you get more out of it if you put more into it. But I'm proof that even very little effort in the book can be helpful. I particularly appreciated Silman's reminders, amidst all the tactics discussions, that self-confidence and a positive attitude are prerequisites for strong play. If you are afraid to lose, or are certain that your opponent will beat you, you are doomed from the start. That is one simple adjustment that every player can make to help their game.