Why an additional double pulley?
This airer had been positioned alongside a wall but a little away from it (about 70cm or 2’3″) in order to clear a dresser.
This meant that at point A the rope was making a 45 degree turn.
This caused chafing with the pulley wheel, which had started to fray the rope.
This picture better shows the turn the rope was making and the distance from the side wall.
By adding an additional double pulley at point B, the turn was significantly reduced, and the fraying stopped.