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.
Jimmy Smith attempts to bring logic, practicality, and good sense to the discipline of bodybuilding. No, really. We're not kidding. This lump actually thinks he can offset years of obfuscation. Oh well, whadda' ya' say we give him a chance?