Economy of force
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 your conflict. No part of a force should ever be left without purpose. The allocation of available combat power to such tasks as limited attacks, defense, delays, deception, or even retrograde operations is measured in order to achieve mass at decisive points elsewhere on the battlefield.
It is one of the nine Principles of War employed by the United States Armed Forces based upon Carl von Clausewitz's approach to warfare. In his words "Every unnecessary expenditure of time, every unnecessary detour, is a waste of power, and therefore contrary to the principles of strategy."