Economy of force is one of the nine Principles of War, based upon Carl von Clausewitz's approach to warfare. It is the principle of employing all available combat power in the most effective way possible, in an attempt to allocate a minimum of essential combat power to any secondary efforts. It is the judicious employment and distribution of forces towards the primary objective of any person's conflict. Economy of force is the reciprocal of mass.
No part of a force should ever be left without purpose. The allocation of available combat power to such tasks, like limited attacks, defense, delays, deception or even retrograde operations is measured, in order to achieve mass at decisive points elsewhere on the battlefield.