I agree with the residual energy hypothesis. In fact that has always been my idea for what most paranormal activity is. Incuding those phenomena we have labelled ghosts, demons, and even angels. Its all energy, folks. Just like us. Just !ike the entire universe. Energy in different forms and of differential levels and strengths and frequencies.
The main deal with most paranormal energy is that it is in fact on such a different level and frequency that it usually cannot be measured or detected with current technology. This is why most men of science do not believe in ghosts, demons, angels, shadow people, et al.
I have problems with the notion that these entities are entirely sentient. Or conscious. Or that they can feel emotions. How would they do this? What medium would they use? We humans use our central nervous system. More soscifie, our brains. More specifically, our minds. Emotions are just the results or different chemical reactions in our brains. Different levels and combination of neurotransmitters, like serotonin and dopamine.
Needless to say, energy residue has none of those things.
I think that when things like shadow people or demons become visible, it is the result of instances of particularly strong or intense energy fields, and they're in the exact optimal environments... Or atmospheric conditions. I also think that so called haunted houses are examples of that.
On both occasions where I personally encountered a demon, the locale was perfectly taylored to foster such an entity of negative energy. I call it Dirty Energy. Onece was in Iraq where I drove a tank in Operation Iraqi Freedom in 2004, and the other was a crime scene house here in Austin about four years ago.