What is the purpose of ghosts? As far as I can see, the only reason for leaving their spirit world and making an appearance in ours, is to frighten us. Why else would they only come out at night?
If this is so, it suggests that the after life is not the higher plane of existence some believe it to be. If knocking people’s ornaments off shelves, or causing their pictures to fall from the walls, or merely making bumping sounds in the night is the best entertainment they can come up with, it only makes one wonder how boring an existence they must have.
I suppose it could be that a spirit is granted a certain status when it first arrives at the afterlife. Those considered more worthy might be given access to more facilities than the less deserving spirits. Would they be given the opportunity to redeem themselves and progress to a more privileged position, I wonder. They surely wouldn’t achieve that by returning to earth in order to scare the daylights out of the living.