I think your question and the explanation given below are contradictory since physical energy is one thing while putting in more effort is something different.
There are very few things in life which, if spent, returns in abundance. For example, love. The more you show your love, the more you get loved. Similarly, physical energy. The more you use it, the more stronger you become. You may call it even "exercise". The less you use it, the more would be your loss!
Now, effort means different. It may be physical, mental, financial or some thing else. You may be able to reduce physical effort to accomplish a job by being innovative, usage of different techniques etc. If you try to reduce your mental effort, then again you will be loosing a lot since higher the mental effort, higher the mental efficiency building.
An efficient Manager puts in a lot of "less" effort to achieve a goal by making his subordinates do the job by using their efforts. Here, no physical energy is involved.