Basically it makes it so that when someone uses a skill, it doesn't necessarily target the person it normally would.

Let's say, for example, that you are hit with a confusion dart. You then want to disarm your opponent. You get a message saying "but he isn't wielding a weapon" because your disarm actually targetted something else in the room.

Assuming that I'm correct in thinking this is what it does (because that's what happened to me once when I was under the influence of one), then it would be good against druids (say) since their sunrays might hit their own treant.

My recollection is it doesn't always do this, but that it can cause it to happen.