Harnesses should be attached to dynamic (stretchy) rope, except possibly when abseiling where the rope is always taut. Falling onto a system consisting entirely of static components e.g. slings over even a very short distance e.g. a metre or two is enough to deliver large forces to the body and possibly cause the equipment to fail altogether. For via ferrata, the harness is attached to lines via a shock absorber that can absorb some of the impact in the event of a fall.