It also involves the situation where the source impedance cannot be changed. Making the phase angle of the load voltage and current equal is desirable. Related topics Batteries store energy. Because of cost, weight, and volume, designs size batteries for efficient extraction of energy. The only case where maximum power extraction is necessary is for short-term, one use items.
Naval torpedoes are one example.
To maximize energy extraction efficiency, the power loss in the internal impedance is minimized. This is done by having the equivalent load resistance significantly higher than the battery impedance. Power utilities , the plug in the wall, supply power to a large number of users. It is not intended to source power to one load. Therefore, as is in batteries, the utility Thevenin impedance is very low and the load impedance is sized to extract the desired power.