Why use a switch if you are using the lights for conspicuousness? I wired the relay trigger to the rear brake power.
Those light are really bright and the beam not well defined. I have mine aimed down quite a bit. I wouldn't use them for supplemental lighting they would blind oncoming drivers.
Well, that second paragraph sort of answers the question. There may be situations where I'd like to turn the lights off. I'd rather have a switch and not need it than to need a switch and not have it.