It's been many years since I was a daily bike commuter. (San Rafael <=> San Francisco.) Obviously, technology is MUCH better today.

However, I came to realize that it was a necessity for me to have two headlights at night, one on my handlebars and one on my helmet. When I left the well-lit urban areas, I was on curvy unlit roads. When I went into a corner, the road went one way and my handlebars (and the light on them) went the other way. It's a bit sphincter-tightening to be descending in a corner and not being able to see the road at all.

With another headlight on my helmet, I could look into the turn and see where I was going.

I also realized another benefit from this. When going straight even in well-lit areas, when I would look at drivers approaching on side streets, I could instantly tell that they saw me when my light lit up their faces.