The Penguin Book of Witches has obvious uses for scholars and students, and enthusiasts and writers may find the book interesting and useful as well. As a fan of fantasy and supernatural fiction, I was intrigued by the premise of the book, and the documents reminded me somewhat of Barbara Michaels' retelling of the Bell Witch story in her book Other Worlds. However, my interest in the subject is somewhat casual, and I didn't find myself wanting to read the book straight through just for pleasure.
Overall, The Penguin Book of Witches is an excellent scholarly resource on a somewhat obscure subject, a good source of information for writers who need details on the topic and time period, and a potentially fascinating read for those with a deep interest in the subject or history buffs who enjoy primary source documents. Those like me who prefer their witches wholly fictional might want to stick with novels and short stories, but may also enjoy the occasional dip into the book.