As readers, as soon as we learn that a story contains elements of anything supernatural, we know all the rules have changed and we can't possibly know what the new rules are. Best of all, neither do the characters! The rug can be pulled out from under any character at any time, and thus, it can shake up the reader and add dimension to the experience of the book.
As a writer, giving my story an occult spin makes me an all-powerful god of sorts. Not only can I manipulate the characters and the situation, but I can manipulate their total reality. I can turn up the evil in villains and the heroism in the protagonists.
I'm having fun with my heroine, the witch character. After a hard bump on her head, suddenly her powers have increased and her magic is now on overdrive. And the villain? She's even more fun with a dash of black magic.
What about you? Do you enjoy reading books with paranormal elements? Do you love it or hate it when the author pulls the rug out from under you?