For me, it's important to take a week off immediately preceding a cycle or blast for the guys that follow that path. Gives your muscles time to heal before the rapid growth they will be enduring. Compared to when I've gone straight into a cycle without a break, I feel much better when I do take a break. Sometimes I've even done 2 weeks if I've been pushin some good weight.
Another great thing to do from time to time is give the smaller muscle groups 2 weeks or so off. Don't isloate bis, tris, delts, traps, or calves. Give yourself 2 weeks of pure bench, deadlift, squats, rows and all the heavy power movements. This usually helps my problems areas (smaller groups) recover and even grow more. This is even ok to do while on cycle. Most guys want to hit the gym as often as possible and slam those bis and tris....but few realize just how much you can grow your bis from a movement like barbell rows. It may take some courage on your part to try this for the first time, but you won't be dissapointed if you do it right.