Energy can not be destroyed, it can only be wasted

While understanding energy efficiency of a system, I think it is important to not only calculate output/input but also look at ways in which the wasted energy (input-output) can be converted into some useful form. For example, waste heat from a foundry can be used to heat water and generate electricity. Heat generated by braking in automobiles can be converted to electricity (Toyota Prius concept). People are going much farther - A gym owner in California has installated fittings beneath the track of treadmills, which convert the pressure energy exerted by the runners in miniscule amount of energy. A famous of brand of running shoes, has installed some piezoelectric (energy owing to pressure exerted) cells in the sole, to generate energy to charge the i-pod or cellphone of the runner.

The last two examples being just a matter of information, the point I am trying to make it is that if we consider the efficiency of any energy consumption system by also looking at all ways in which the wasted components can be converted to usable forms, we will have a better view of the efficiency of the system. In fact, that is the way, we need to judge a system's energy efficiency and not just by calculating main output/ input.