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.
Girls may hate to see you leave, but if you've got a broad back, they'll love to watch you go. (Course it helps if you've got a nice ass, too, but that's a whole 'nother article.) Mike Robertson is here to troubleshoot your rowing.