Entity or not, some of those things on "Ghost Hunters" are just plain creepy.
You might be all right to live without a lease in a temporary place, Marc, but long-term, and especially if you're going to be harboring ne'er-do-well homies on a regular basis, a lease is a good idea. The point about busted pipes or a breakin is also a valid one. If your plan is to move out when something like that happens, then you'll be all right. But you got to have a plan. You got to know the ground rules or some people will make them up as they go along, and screw you when they can.
Don't be a Rodent.