The use? The use, they ask? The use is light as fuel for light speed travel.
Apologies, to clarify, one of examples used to demonstrate faster than light travel, well, the inability of it, is the light on the front of a locomotive, doesn't move faster than the speed of light. With this new discovery, the light could be "attached" to the rear of the locomotive, like an outboard on a boat, to push the vehicle at the speed of light.