Recovery is a critical component of a fitness program. When I was in high school, our basketball mantra was 4-6-12. It meant practice 4 hours a day, 6 days a week, 12 months a year. (At least it wasn't 24/7). Anyway for several years I pretty much did that. My attitude was that I'd work harder than the competition and would spend more time in the gym. I benefited from the intense commitment to basketball, but I didn't understand the dangers of over training until years later.
During my senior year, my conditioning and performance peaked mid season due to over training. Towards the end of the season and during State Championships I felt exhausted. I could still perform okay, but I fatigued quicker and took longer to recover from injuries. I didn't realize at the time, but I had been over training and had not allowed my body sufficient time to recover.
Occasionally people will notice that they can actually lift more weight, run faster, or jump higher after coming back from a vacation or after taking several days off from exercise. It is important to remember that when you work out, the process literally tears your body down on a microscopic level and you need proper nutrients and rest for your body to rebuild and recuperate. Many people find that as they age, they also require more time to recuperate between workouts. Other factors that can affect recovery time include your nutrition, stress levels, intensity and frequency of workouts, and how much sleep you get.
Remember that you don't want to work the same muscles with intense workouts without allowing them time to recover. Too much exercise without sufficient rest can stress your body and make you susceptible to injury or illness so give your body what it needs to recover.