Heavy trucks are no joke. They are often huge, eat fuel in barrels, and may weight like a light aircraft. However there are some tasks out there that none, but those monsters may handle. Transporting oversized cargo into the deepest of bogs or rescuing an off-road truck, full of valuable cargo from the huge pile of snow, or salvaging a broken vehicle from the fast mountain river. These are the kinds of tasks Heavy Trucks are good at.
They may also transport your default cargo containers from point A to point B of course. If you have the fuel to do so.