Metaphysical Ecology is important. There is a reason that Supernatural Beasties do what they do. There may be a wellspring of energy that is tappable and has not yet run out, in which case, if these creatures are powered and fed by it, their reasons for what they do may be entirely arbitrary. But if, instead, what the entities require to continue to exist is not easily and freely available, then you have an avenue through which to discover certain hidden characteristics of reality. If they torment because they feed off of, say, pain, then the implication is that there is a whole section of physics not yet explored. That is, unless they are ultra-efficient and just feed off of phermones or minute, but specific, perturbations in electric fields. In that case, you'd have an amazing test subject with which to research increasing input-output energy generation. But if there is a connection between the "Spiritual" and the "Physical", you could study it. It would be a science. Before you can study it, though, there have to be distinct objects and events which can be observed, which is where supernatural creatures come in handy. If there ARE ghosts, angels, demons, or so on, then there has to be an energy to support them. If the energy is human-based, we've got a lot of potential for some really wacky events if we so choose as well as a potentially concrete reflection of the human psyche with which we can gauge the state of the "Universal Subconscious", though if they merely FEED from the energy and the state of mind wherein the energy was produced is irrelevant, then what we have is a large reservoir of energy that we could redivert to our own purposes. If the energy does NOT come from homo sapiens, then we would have a new insight into the workings of things and a possible new resource to tap. If the energy has strange new properties, all the better to comprehend the universe with and make crazy new toys out of.