I have heard of running the monitor system's polarity opposite that of the mains, but that's something different than what's being talked about here.
This is a good idea. Because the monitors are facing the opposite way of the mains, you want to make sure all drivers move the same direction.
OK, sarcasm is now turned off.
But I have heard more than one car stereo installer insist that the right door loudspeaker should be wired with polarity opposite the left door loudspeaker. That way they will be in phase. Seriously.