Hello!
You would want to turn on your headlights. When it is sunrise it could be foggy outside. So for cars in front or behind you to know you are there, you would need to have your lights on. after sunset, it is obvious as to why you need your headlights on. If you don't have them on, nobody can see you which will end in an accident (which will most likely be your fault.)
I hope this helped!
I am, yours most sincerely,
SuperHelperThingy