A bit of a niche query, but one I've been thinking about recently, and I'd be interested to hear that others think.
I write ghost stories as a sort of hobby, and I usually try to provide some kind of backstory for the ghost, i.e. how the person died and why they're still haunting the house/person/object. Sometimes I find that this makes it rather heavy on the exposition, and there has to be an unlikely plot device to reveal the backstory in the first place (I know ghosts are inherently unlikely, but you don't want too many contrivances in one place).
So when you're reading a spooky story, do you like/need to know the background stuff in order to enjoy it, or are you happy for it to remain unexplained as long as the story is engaging enough? Do you find it frustrating if you get to the end without there being a "why"?