Since owning this book I've found myself turning to it for explanations and examples over the required text. Almost every section lists definitions of terms, a bunch of useful facts and fully worked examples. Explanations and examples are clear and concise, while the facts often help to understand the process involved before getting into the examples.
I'd like to stress that this is certainly no replacement for a text book in discrete/combinatorial mathematics, however it is marvelous to have by your side to provide additional help through problem areas.