A superb book with many valuable recommendations and tips for writing well-structured business documents. The framework described in it is highly effective in any non-narrative writing and it is used in most top-class consultancy firms.
The book is also good for gaining some insight on hypothesis-led problem solving, both in the case of inductive and in the case of deductive reasoning. In this respect, it is full of examples that challenge unstructured and unorganized thinking and writing.
It may be however useful to complement it with other books on creative thinking (e.g. Edward De Bono's), mind-maps (e.g. Tony Buzan's), and psycho-linguistic approaches (e.g. NLP, TA, etc.)