Well, all right, if you want to be technical ; ) ...you don't have to read "the book", online is sufficient.
Reading Alexandra's letters (in their complete form) contradict much of what is said about her. Griffh has covered it far more extensively than I ever could in his "Empress Alexandra Fights Back" threads, so I just say that perhaps people would not be so quick to accuse her of things like being Rasputin's lover, or "making" Nicholas change ministers, or being a German spy.
Teddy, to answer your question, reading the complete letters is invaluable. So many times we read bits and parts, often in context of someone else's statement or point of view, and when you read the whole thing, you understand what she was "really" saying. I believe that if someone is going to write a book or article about someone like the Empress who is so maligned and misunderstood, using a reference such as this will offer insight like nothing else into the actual person. Even their diaries are insufficient, since they used them to record facts, not emotion, which makes them seem cold and uncaring, even inhumane.
