From SKYbrary Wiki
On many aircraft types, reverse thrust capability is installed to augment wheel brakes in decelerating the aircraft. This feature can significantly increase deceleration rates and reduce landing distance or, in the event of a rejected take off, reduce stopping distance. On some aircraft, reverse thrust can be used to enable the aircraft to back up under its own power. On a limited number of aircraft types, such as the C17 Globemaster, reverse thrust can be utilised in flight to significantly increase descent rate without a corresponding increase in airspeed.