The Hammer Strength unilateral supinated-grip pulldown is one of my favorite machines. It's nearly impossible to duplicate with free weights what this machine can do.
Several training methods work great on this machine, like maximum tension alternating pulls (hold one side isometrically in the contracted position at the bottom while the other side is moving). It also works great with bands for added accommodating resistance.
With mechanical drop sets, instead of reducing the load, you switch to a new but similar exercise by changing the grip, angle, etc. The result is a whole lot of burning and a whole lot of growth.