The question was: which side to place a cutout switch for power from a battery to the system; In this situation it would be the positive side that should be switched. Line Kill.
The other way, If any other wire ever came back to the battery ground side you could short back to the ground, dangerous. If you wanted to run any accessory and wanted to keep power to it you would have to do that.
Second: These switches are not designed for exposure to water or heat and tend to decompose when exposed, when they decompose they tend to either leave you by the roadside with a propped up thumb or burn your car up or burn your car up and burn your shop up with your car, or electrocute the s-it out of you when you flip the switch.
So, first, don't be a cheap a-- and buy a junk one, second mount it where its not gonna get wet and or hot or salty, oh yes and third inspect it for any signs of corrosion and replace it and sell the used one at a swap meet to a Chevy guy.