QUOTE=Daily Commute]On the road, cars treat me differently with an HID headlight. The extra bright light helps me to see exactly what that dark smudge on the road is. It also helps me to ID potholes and other cracks much more easily. On the trail, the HID makes a huge difference because I can see overhanging branches and can see road conditions. It is particularly helpful in the rain. When it gets icy and snowy, the light will make even more of a difference.

Good point, well explained. Better than my explanation really.

There are many times when a bright light is not needed, for most things really. To see an animal or a person it's pretty easy with just about anything. I specifically bought my bright light for really only some conditions like you say small holes smudges etc.

When going fast on my expensive bike that has a $850 wheel set, 23 mm tires thin as paper,( yes Kevlar belt) I want to see every tiny pavement variation. I am very careful about getting flats. I don't want to damage a wheel. Because I have a bright light, I can see tiny specks of glass that I would go right over with other tires. I can see the glass, a crack in the pavement, sand, oil, etc.
And as you say exactly, when the oncoming traffic is bright and there is a lot of ambient light, if you want to see the tiny bits of glass you need huge power. That's really what I bought the light for, not other easier situations. It works, I got one flat this year on that bike in 3,000 miles, it was when I was not looking. I hit a small rock. when I look it's OK. I got one flat on that bike the last two years also, about 6,000 miles.

Riding down an unlit bike path is different, my eyes adjust, and if I have stronger tires I can get by with my LED light. If I rode my mountain bike all the time on the road, I would really not even need it. But it really does help off road, on fast descents on loose surfaces.

For a lot of situations it is not needed. For many types of riding it is not needed.