Some lifters have trouble hitting their backs, even with back exercises. Often, the biceps take over. The unilateral lat pulldown allows you to really focus on the back one side at a time.
Do not fully extend the arm at the top of the movement.
Chad thinks it's time to cut the crap about motor unit recruitment. He feels there's a fundamental misunderstanding about the subject and he doesn't know whether the truth was simply forgotten, or never learned in the first place.