When charging a car battery, when should the black negative terminal never be connected to the negative post?

This is for a negatively grounded vehicle of course. I've always charged a battery with red clamp to the positive battery terminal and the black to ground, using lug or metal body part. I was told recently that the black clamp can go to the negative terminal, but I do remember experts saying to never connect black to the battery. Is there a specific case for this, like jump starting? I even had permanent quick disconnect rings attached by a dealer and they attached black to the negative post and they said that that was perfectly acceptable.