While exercise is important for all and training is essential for any athlete, it is also okay to take a break every once in a while. Restis an important principle of exercise.
When strength training, you should allow yourself 48 hours before working those same muscle groups again. Even when performing cardio exercises, such as running or biking, it is a good idea to rest at least one day a week.
Rest allows your muscles to adequately repair themselves. Continuous or prolonged use without the time to fully rest and rebuild can actually weaken muscles, ligaments, and tendons and lead to injury.
Psychologically, rest also allows you to re-energize and prepare for future workouts.