Spirits are whole, we are only whole when grounded in our bodies (because we are tied to it). If our spirits could leave 100%, our bodies would die. But thankfully, it doesn't work like that, and its impossible to leave 100% while projecting. Otherwise newbie magick practioners would be dying left and right.
When we AP, we only send out a small percentage of our energy out along with our consciousness. When we etheric project, more energy leaves to travel and the awareness of our body is absolutely nothing. So if astral projection is...say 25% of your energy out, etheric would be 65%. If you do not know what etheric projection is, google is your friend. It is not as easy as AP and has more dangers involved. So tred carefully in that subject.
I personally just call it journeying, as I was taught to know it by as a child. And it includes anything from astral projecting, etheric projecting, mental projecting, dreamwalking, and visions. One word...beautiful simplicity. But new agers like their technical terms and unfortunately most information found will be under them, not mine.
When spirits poltergeist, they either do it at a time or place that the veil is thin, so it isn't much effort. When a spirit poltergeists without a thin veil, they have to gather energy from physical sources (electricity or physical people). That's why I said it would have to be under the right conditions. Even spirits must have the right conditions.