The key is to find a saddle which encourages the correct riding position which is comfortable for the rider.  It's recommended that there are 4 inches in front of the rider to the front of the saddle and 4 inches behind the rider to the back of the saddle with the rider sitting in the centre of the saddle in the correct position (line from shoulder, hip to heel for dressage; shoulder, knee, toe for jumping position.)

Key exception to this rule is putting tall, thin riders into small seated saddles which results in the rider's knee being interfered by the knee roll and forcing the rider to sit too far back in the saddle.  This creates an increased pressure on the back of the saddle for the horse levering the panel on the horses back.