Well, its adhesive so when youre applying it to something that was painted, if the paint-plastic/metal bond isnt as strong as the vinyl-paint bond, then yeah youre going to lose the finish.
On painted body panels, you really dont have to worry unless the paint was f'ed up/paint prep sucked.
You cant just go peeling it cold, though. We heated it with a torch and heat gun and it came right off. A simple clay/polish/wax on the roof and you could never tell it had anythign on it.