Lets say you're driving a car, you get hit in the bumper, your bumper's forgeted up. If you had the skill in metalworking, you'd be able to change it back to it originally was.
Possibly, but depending on the dent you may need to have specialized equipment. Once something gets dented, it wraps the material and causes indents. Like if you take a soda can and push lightly on one of the sides, it will get pushed in. If you pop the dent out, you still have the warped areas where the dent was. These can be quite the pain to remove and restore back to the way it was.
Depending on impact speeds, you would also need to check other areas of the car to make sure nothing else needs replacing.