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.
Most of us poor slobs have jobs so we don't have the luxury of doing two-a-days, but we figure since it's summer there are a bunch of feckless college students out there doing one bong hit after another who just might be able to take advantage of this program.