Here in the wide open spaces it's essential, especially when people DON'T turn on their lights in rain, snow, fog, etc. But also people who drive a white car across a desert often blend into the background as if that were snow until they are right on top of you. Heat waves distort the view as you watch out ahead.

Put the lights on all the time! Newer cars here have "daylight running lights" as a default setting; my only complaint is that they don't also turn on tail lights.