Let's talk Engineering! How would you connect a switch in a circuit - on the positive or negative terminal?

In real sense, whether the switch is placed on the negative or positive terminal, it will still work; but it is safer to connect a switch on the positive terminal.

Usually the negative terminal of the voltage source is considered Zero Volts, or Ground. In that case, the switch in the positive feed will remove all power from the load. If the switch was in the negative side, the load would still have power applied, and an accidental ground somewhere could cause unpleasant surprises!