Except that in most countries there are more than two candidates/parties.
Not to mention that you can't really take it on the honour system (since it's to your obvious political interest to vote while your partner doesn't, or to "pair up" with multiple opposition voters without telling them), so you need a system that guarantees that people keep their side of the deal. And if you're setting up an extra system just to keep track of mutually cancelled votes, you're just setting up a more complicated version of the system for the same results. That's the
opposite of more efficient.
But perhaps I am overanalysing a comic.
