For headlights specifically: both. A cleaner/clearer lens will greatly improve headlight brightness assuming everything else is working as intended.
If you have a car that has headlights like the before pic on this post, I'd highly recommend grabbing a kit.
Also the box said 10 horsepower.
I reckon they could only run with that claim as long as the tires of the time were still crappy! Now imagine any of the Big 3's big hitters on some brand new Pilot Cup tires - my god.