Sleep is necessary. Do you mean does sleeping stunt muscle growth and overall health? Not at all. In fact, sufficient (7-8 hours) of good sleep daily is essential for good health and good mental condition.
Yes. There are several phases of sleep and one of the most important levels for maximum rest and renovation is delta phase. This is the deepest level of sleep in which hgh (human growth hormone) is released and in adults provides one of the most potented hormones that naturally helps prevent tissue and organ breakdown.