Too much rest can sometimes be just as bad as too little. When you workout, you tear muscle fibers. Rest allows your body to rebuild the muscle fibers. Given enough rest, and the muscle fibers will be stronger than the ones that you tore. Given too much rest, and your body will decide that it does not need the extra muscle mass and will begin to break the muscle fibers down again.
Check Out: Avoid Too Much Or Too Little Rest Between Workouts For Optimum Performance Gains