I agree, rest and recovery is IMPORTANT!
From personal experience. I used to do 4 hour workouts everyday because I was addicted to going to the gym. I was not getting enough recovery time. I ate like a horse, but actually started losing mass and weight instead of gaining because of catabolism. I was toned as fuck and my muscles looked like wire cables, my veins were popping out all over the place, but I kept losing mass and weight. I looked like the Cambodian entry in a BB contest. Like a dummy, I thought it meant I had to work harder. It wasn't until one of the trainers in the gym started noticing me there everyday for those long hours and told me that it wasn't very healthy and explained it to me. I went from 160 to 130# It scared the crap out of me. Now I only work out 3 times a week and never more than 60 minutes and I'm back up to 150#. Not as wiry or defined as I was, but I certainly look and feel healhtier.
If you're worried about plateauing, the cure for that is changing up your exercises and routines, not overtraining.