Its a constitutional thing. And think back to 2000. As soon as Cheney agreed to be Bush’s VP he changed his residence from Texas to Wyoming. Now, I wonder why he did that?
I'm guessing to allow Texas electors to cast their votes for Bush. I think the 12th Amendment forbids a state's electors for voting for both President and Vice President if they are both from the same state as the electors, but I don't know of any prohibition on it, do you?