I would think the reasoning behind its common place is to give scum a more fair shot at being able to kill someone through town protection and/or a bodyguard among other things. It seems like a tool that is often abused far too fast in games, imo, but one that should be saved for a proper time. That's why when I've used it, I've usually said it counts as your nightkill for the night, making people think about when to use it a bit better, as they don't consider it a second kill at that point.
That's my two cents, anyway.
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Xbox GT: PrivateBiscuit1
Down with Zhang. Let there be Biscuit!