... performance is efficiency

Do what you do, do it with the maximum of effect and the minimum of effort. A good guiding principle for any systems management. Provided you meet the service standards, then minimizing costs should be the priority. Costly overprovision of service can damage your ability to invest in other innovations.

Take the example of a football player, he scores a goal by investing effort in running up and down the pitch. But too much running early in the game will impact his ability to score later in the game. His performance is measured over the whole game; efficiency of his own game has a direct impact on that performance.

So it is with systems. Cost/effectiveness service provision is only possible when you understand how much running that system has to do - and what goals need to be scored.