The chores on earth are done and it's time to move on. Vengeance is a strong motive for a ghost to continue to hang around after the final curtain. The vengeful ghost is angry at some treachery done him. Perhaps this ghost is the victim of foul play so he continues to haunt a specific locale in hopes of letting the world in on his killer's identity. A few years ago a very famous murder case was solved in just this way.
Some people believe that the vengeful ghost is the only true ghost there is.
A poltergeist is a very disturbing prankster who throws things about, rattles windows, and in general raises havoc in the home it has decided to take up residence in. Dealing with a poltergeist can be difficult, time consuming, and all but impossible. I'd pack my bags. In some cases, it might be better to move on than to deal with this type of haunt. There are ghost hunters who claim that the very word ghost is a misnomer.