Climax beads are the best way to go to reduce the rh% - they have 65 and 70% beads. The beads will hold the humidity damn near right at what they're designed to.

As far as why you'd want to go below 70% - 65 is actually more ideal with some cigars. ISOM's seem to smoke better kept on the drier side (60-65%). I've found that keeping cigars at 70% tends to cause burn problems. I try to keep mine at 65% and other than an occasional loose wrapper (which seems to be more related to the manufacturer than humidity), my cigars smoke very nice.

I have a Diamond Crown humidifier in my main humidor. I can close the shutters and reduce the rh - I'm able keep it right around 65% and seems to do very well at that.