According to the information found under "theories of why we sleep," what is the energy conservation theory of sleep?

The energy conservation theory of sleep is just as it sounds; we save energy by sleeping, resulting in needing less energy. While it is true that our caloric needs and metabolism are reduced when we sleep, it is not fully known if this has a significant impact on the preservation of our energy. Research in favor of this theory relies heavily on studies done on animals that hibernate. Hibernation lowers an animals heart rate and burns less calories, much like sleep does in a human. Animals tend to hibernate in order to conserve energy when there is a scarcity of food, like in the winter months. Based on the conservation of energy during hibernation, due to the reduction in an animals physiological responses; it is said that sleep in humans is a form of conserving energy. However; it is often argued that the amount of energy saved during sleep is so minuscule, that sleeps primary function is not for energy conservation.