There is so much about the brain and its complex workings that we do not understand. Every time an expert explains a little more, learnt through scientific study and controlled experiments, this becomes quite helpful.
I found the book particularly useful as it it very well written, very readable and informative; at the same time, it is not too technical (except for a few small sections) for the lay person. The author takes on a number of the “strange” phenomena witnessed in the world head-on (such as sensed presences, experienced by athletes, mountaineers and in Charles Lindburgh’s transatlantic flight), describing real, specific examples, and explains what goes on in the brain during those times. The way human brains work gives us the tendency to look for patterns and infuse them with meaning (whether correct or not).
Michael Shermer also presents in some detail, the various cognitive biases that affect us when forming beliefs. Most of us are vaguely aware of some of this (e.g. anchoring bias and framing effects) but having such a comprehensive list explained is very helpful. I see the usefulness of applying this knowledge whenever we are presented with a persuasive argument, thinking about what traps we may be falling into.