Flood is nice when crawling up singletrack switchbacks in the dark, or picking through other technical stuff. I used to set my dual-beam NiteRider's bracket one click above its lowest aim, and then I'd drop it down to the lowest notch to aim it right in front of the bike, and switch to 20W flood to help pick my line through slow, tricky stuff, despite the bars weaving. The even spread of light from the flood beam was just the ticket. Although I just got one of those Minoura Besso mounts and attached it to the side of my headtube, so now the bars can weave and the light will still aim where the bike's frame is pointing.

How relevant is that to the OP, I don't know But it's the best use I've found for a full flood beam.