I frequently have my headlight in flash mode. As others have noted, this tends to be more noticed against the usual street backdrop of steady lights. Someone waiting at a cross street or driveway (or planning to turn left into one) might otherwise think my rather dim light (compared to car headlights) is from a much more distant car or motorcycle and pull out into my path. The flashing mode is also more conserving of battery power.

When I get off the road onto MUPs I switch to the constant mode for better illumination of the path and to avoid annoying pedestrians with the flash pattern.