Many years ago it was said that having lights on during the day increased your visibility to other drivers. These days with better batteries, lights, etc. it's no problem to keep them on. For a while it was a law for motorcycles to burn headlights during the day. I live off of a frontage road with trees down both sides. When I'm trying to turn onto the road, because of thick trees it is very dark down the road unless the sun is right overhead. Combine that with a dark colored car coming fast and trying to get a break in traffic from the other direction and just getting on the road gets chancy. I like to see people with their lights on, it makes me feel much better.