Have you ever given any thought to how far you can see at night as you are driving along down the highway? High beam headlights seem to overpower the dark, but there are a lot of situations where we are limited to using just the low beams. I was required to calculate the safe speed using only low beam headlights at a seminar and I was surprised at the result.
Most drivers can see a dark object at night with low beam headlamps at a distance of 24 to 25 metres. The average perception/reaction time is about a second and a half. Using these facts, the result is a speed of 38 kilometres per hour. If you travel any faster, or don't pay full attention, you will collide with the object before stopping.
Dark objects such as pedestrians and deer are commonly found on the roads we travel at night. Granted, there is other light to see by in town, but out of town approaching and passing other vehicles we are hurtling along at 80 and 90 or more, and using only the low beams. This seems to be a compelling reason to be a little more careful with our speed at night to me.
Now consider what could happen if one of your headlights were not working, or that both were so coated with dirt from winter driving that the full light output was not available. Complaints about vehicles with only one headlight are common and one only has to observe and count to see that this is true. For your own safety it is well worth the time and money to keep your headlights clean and in proper working order.