Um… to enable you to perform defensive maneuvers.
Except for Gryphons, who have this as a faction ability, there is no way for you to easily redistribute troops between turfs you control—and this is by design.
Unicorns can defensively maneuver troops from one adjacent turf when attacked.

Further, if you find you’ve spread yourself too thin or wish to consolidate troop strength in certain areas, this Action Card enables you to achieve this.