Each time you work out, you need to rest between sets.
And not only between sets. The idea is to work out intensely, and then get out of the gym and grow. Many lifters complain that their routines aren't working. But the biggest problem is they are overtraining and not getting enough rest between workouts. The body needs ample time to recuperate and repair itself from workouts. Never, never overtrain. And whenever feasible, get a full body massage. I do so once a week. Massages not only feel great but they speed healing.
Just as too little exercise won't stimulate your muscles to grow, too much exercise won't work either. For ectomorphs like me, 48 hours between workouts is the absolute minimum rest I should get. The body needs to be fully recovered from the last workout before working the same body parts. As for sleep, I am in bed from at least 10:00 pm to 6:00 am every night. I used to get by on 8 hours of sleep per night but now it's more like 9 hours because I've upped my workouts. I also nap for an hour on those days I lift (like today). Plus, I always take one if not two days off each week from doing any kind of exercise. As I said, most lifters are overtrained, so the extra rest won't hurt us. In fact, it will probably help.
My goal is still to climb the Alps this summer. Will my body be in shape for that adventure? Will I be able to arrive in Zermatt fit -- and rested? Stay tuned!