Some saddles tend to slide back as the horse moves, particularly if the withers are high or there is a dip in the back behind the withers. Pulling a saddle forward before mounting would not be recommended as the saddle is moving against the hair. If enough hair is affected, or the horse is ridden for a long time, irritation with the potential for a saddle sore can occur. The need to move a saddle forward may indicate the saddle doesn't fit the horse's back.
