The lock screw on my Phantom MUST be locked down because when loosened, the tonearm tilts to one side slightly due to play in the ground body that moves up and down in the tower. If I don't tighten it, the whole assembly is tilted so azimuth and spindle to pivot are off. I don't see how contact from a single point set screw would make a sonic difference, but I think it makes more sense to lock it down given the level of fit I have on my tonearm.
