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.
Mike Mahler knows a lot of training bad asses but he thinks they're complete pushovers in their personal life. They avoid risk and couldn't make a tough decision if their lives depended on it. He wants to change that.