You probably never gave it much thought, but how you train back is unlike the way you train other muscle groups in your body. Why? Most notably, almost all the exercises you do for your back are done bilaterally, meaning you work the right and left sides of your back at the same time. In fact, it's probably rare for you to include dumbbells and one-handed cable moves in your back training, with one-arm dumbbell rows being the likely exception.
Isolating each side of the back by doing unilateral movements affords a number of benefits, namely allowing greater isolation of a particular area and ensuring balanced development because one side can't compensate for the other during a move. In addition, unilateral movements allow you to produce more force on each side of the body and work through a longer range of motion than is the case with bilateral movements—both great ways to shock the muscles into growth.