When you need to cut heavy sheet metal, like the fire-rated door cover that we saw in this TV show, regular shears are not good enough. You could do it with a metal cutting blade in a jig saw, but that is very slow.
The professional will use electric shears that make the job easy, but they are of course very expensive.
If the metal is even heavier, the pro uses a gadget called a nibbler that actually chews out pieces of metal so that the tool can pass without having to bend up one side of the cut.
And if it gets thicker than that, then the pro will use a torch to cut through.
It all depends on the thickness of the metal and the speed with which you want to work. If you have too much metal to cut with that slow DIY jigsaw, check out renting one of the other tools.