The light from beam headlights may cause glare. That is why you must use low beam headlights when you meet oncoming vehicles or approach another vehicle from behind. You should also use low beams in lighted areas, such as cities. To avoid blinding yourself you should also use low beams when driving in fog, heavy rain, or snow.
You must turn on headlights 30 minutes after sunset and 30 minutes before sunrise. Why is it 30 minutes after sunset and not before? Wouldn't it be more logical to turn on your headlights before sunset? I mean, isn't it dark as soon as the sun sets?