Ultimately the main advice of the books boils down to: "Don't talk to the police." This doesn't make it useless, however. The basic advice is worth repeating and the book offers an insight in techniques that might be employed by your adversaries to break your silence, as well as methods to help you resist those attempts. It's worth knowing in advance what to expect and how best to behave. Acting in accordance with your own values and desires is generally easier when you have sufficient information.