It's harmless. Great way to get somebody to talk, too. We do it to our troops in evasion training. It sucks when it's happening, but there are no lasting effects. It's no different than turning up or down the thermostat or pumping in loud music for hours on end. That being said, there is a time and a place. For it to remain effective, it should only be used when needed. If time is of the essence and there is no doubt that somebody is a bad guy. If there is doubt, it should be off the table. Though, would you really shed a tear if cops did it to gang-bangers?