The breast augmentation procedure is designed to increase the volume of the breasts. It's understandable to consider how that volume increase may affect breast shape and height. Fuller breasts may, in fact, very subtly fill out deflated skin to provide some degree of lift. That said, the degree of lift that can be accomplished with breast implants is usually not sufficient enough to offset the risks of augmentation performed to fix saggy breasts.
Whether you choose saline or silicone breast implants, these devices have weight to them. This means that your breasts will be heavier after your breast augmentation and will thus tug on the skin. If you receive implants without a lift and you already have some breast ptosis, the problem may worsen sooner than it would if you also undergo a breast lift.