I will quote Montague Summers, from his introduction (Summers' introductions are always as delightful as they are creepy), "To the historian, to the occult student, Guazzo's work is of incalculable worth."
That would sum it up, I think. Reading this book gives insight into the ideology of those who believed in witchcraft at the time and the obsessive depth of how they'd invent perverse fictional "facts." The insight of reading someone like Summers, introducing the work, shows us just how persecution works.... you can see it in our political era. A "believer" in this kind of thing believes because they want to, because it makes sense on some unconscious level of desire. You can see it in Summers, who is okay with disputing that "some" of the work about witches might be suspect, but overall he mostly believes... just as someone might see a video of an ICE agent killing someone in mindless rage, and without justification, but that person seeing it still supports the idea of targeting immigrants, so the lack of sensible connection between the two is overcome by the irrational unconscious connection.
Oops, I made this post about the book turn into a political rant. But that's not entirely inappropriate... what was witch persecution if not a collective fantasy and redirection of hate and fear, just as today's political arena...