One of the most commonly misunderstood topics of breast enhancement surgery is the issue of sag, and the assumption that breast implants help the problem.
Many women have sagging breasts that they want improved, and not all of them have it as a result of pregnancy, breast feeding, or weight loss although those are the most common factors. To understand the topic, a distinction needs to be made between ptosis (sag) and involution. Ptosis usually means dropping of the nipple below its natural and ideal position, while involution is more of an "empty-bag" appearance, where the nipple may still be in an anatomically normal position. Of course, both things could be going on.
An implant alone may be all that's needed if the problem is only involution, but when there is nipple ptosis, a breast lift (mastopexy) needs to be done. If the lift isn't done, a "snoopy dog" deformity can result, with the breast tissue "hanging" off the implant - not a good look. The lift and implants can usually be done simultaneously, but if there is significant ptosis, it is best to do the lift first, then the implants later.
The type of lift depends on the degree of ptosis. It is essentially a geometric problem that needs to be solved, based on how much skin needs to be removed for the lift. The typical scars that result range from a circle around the areola (periareolar or concentric mastopexy), a lollipop shape (vertical - the most common in my practice), or anchor (standard mastopexy). Beware of surgeons who routinely do the anchor shape mastopexy on everyone who needs a lift.