From what I understand of the shed process they have a layer of liquid that forms between the old, soon to be shed skin and the new stuff underneath. Soaking may actually mess up this by leeching out that liquid through osmosis. Soaking is best left for sheds that don't naturally come off complete. Soaking also stresses your snake so use it only if really needed. Quite a lot of snakes will defecate during shed and you may even find a lovely stinky "present" wrapped up in their shed.