As everyone else has already said, it's been shown that it actually helps to reduce traffic accidents. I was unaware until this thread that it was legally mandatory in so many other places, but around where I live, there have always been "daytime headlight corridors," sections of roads and highways with signs up informing drivers their headlights should be on for the next however many miles/kilometers. I was told that their purpose was to study whether daytime headlights did in fact help in a statistically significant way. But I'm pretty sure that had already been established a long while back, and the corridors are just particularly dangerous stretches of highway with no physical barrier separating on-coming traffic, making daytime headlights along that section of road a very good idea.