Military, coast guard and law enforcement personal all have access to and find uses for both road and signal flares. In any case, the ability to pop a smoking flare can be used to signal aircraft, mark accident boundaries on a dark road or be used as an emergency disposable light source.
Though not used often in Airsoft, it can be nice to add to a loadout kit which is built to emulate a more expeditionary soldier or emergency response team. In some unique cases of course, Airsoft events might well make use of flare for illumination or thematic purposes. They make decent mini umbrella holders too.
Milspex offers an affordable line of MOLLE strapped signal flare pouches with clip-buckle sealed lids, we offer them in a variety of milspec style colors.