Recuperation is the time it takes the body to recover from hard intense exercise allowing it to get stronger, to change its form (gain muscle, lose fat), and to sustain motivation. Effecting body composition change, including strength and muscle gains, abound during rest periods - 23 hours after training.
Recovery after exercise is necessary for five reasons. One, to allow the nervous system to recuperate (neurological). (When a person becomes stronger a day or two after exercise it is a neurological adaptation, not a physiological one.) Two, to permit sufficient “supercompensation” to take place and forge the process of body composition change. Three, to stimulate muscle growth (physiological). Four, to regenerate the whole body (mental, physical, psychological) so it may be renewed with energy and vigor by allowing stress to dissipate. And five, to sustain motivation (psychological), conceding that one follows the right routine, exercises with the right amount of intensity, and uses the right training method.