Cable pullovers allow for a great stretch and full contraction of the lats. The added benefit of having your entire back supported by lying on the ground lets you focus on volume without the fatigue accrued by supporting yourself.
Remember, big lifts first, then do this low-stress finisher for added volume.
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.