Wrench does flatten ropes and sure as hell milks them hard. Hence milking new ropes. Ropes will last way longer if only used with a runner. During rec climbs I have glazed so many ropes messing with huge descending swings and bombing around. The prussic heat of my michoacan destroys covers so I have resorted to using runners when rec climbing as you cannot glaze ropes with them. My michoacan hitches are loose.