All it does is provide the closest path to ground available for the lightning. It doesn't have to be a large conductor. When the lightning destroys it who cares, it did it's job. At least the lightning wasn't looking for another more meandering path. It without a doubt decreases the chances of the lightning going through passengers or frying computers/circuits. I have seen them plenty of times. You likely didn't notice them before because you didn't know what they were.