Even on the road they can be handy. Doing switchbacks when your bike light just disappears over the edge of nothingness... having to do little bar swings to 'flash' the corners in the hope of seeing the apex, the edge, anything.
I have a Joystick and a Diablo now and use them for road and dirt races, in combo with Supernova or Maxx-D / Six Pack if I'm doing batteries.
I rode from Broomfield to NCAR Boulder to see the dawn sunrise, long wide roads with zero lighting. Had a light on the bars, light on the seat post, Garmin on the bars as well to show me where to go - and went straight past a six lane turn because it was just outside the little lozenge of light that was surrounding me.
Riding back in the daylight I was amazed, but simply didn't (couldn't) see it at night.
I rode from Broomfield to NCAR Boulder to see the dawn sunrise, long wide roads with zero lighting. Had a light on the bars, light on the seat post, Garmin on the bars as well to show me where to go - and went straight past a six lane turn because it was just outside the little lozenge of light that was surrounding me.
Riding back in the daylight I was amazed, but simply didn't (couldn't) see it at night.