Switching on ground

I was told by the owner of Billet Automotive Buttons, to switch the RGB buttons on ground as that is how they are designed, and that for my line lock solenoid, boost controller solenoid, etc, I would switch on ground.

With AC, switching on ground is extremely dangerous, so is DC different and is it commonly acceptable to switch on ground without a relay? I'd really prefer not to use a relay as I don't have room to redesign the layout considering I have my panel, distribution boxes, and initial key-on relay already in position.

Thank you.

I think I've got it. In older vehicles, some are positive grounded, and now modern are negative grounded. Since voltage is calculated by potential difference from ground, a negative (or positive for that matter) grounded vehicle, is only grounded in terms of the battery cell, and has no relationship to Earth.

With that in mind, then there would not be a potential difference between the vehicle and ground (or us)...only the batterie's cell. In that case, switching on ground is no different than switching on hot. At least that is how I understand it now.