Breast implants aren't the only answer to every boob problem, especially when it comes to saggy breasts. To explain this using imaginary visual aids, if you put a bowling ball into a nylon stocking, you wouldn't expect the stocking to shrink, would you? Well, your breast skin and tissue are quite nylon-like in some ways. Stretching and gravity can cause runs (in this case, stretch marks) and a loss of elasticity. In our little metaphor, that translates to the dreaded droopy boob.
So back to the breast implant question. If your breasts are already sagging, why would you aggravate them by stuffing excess weight into them? You'll only wind up looking like Charo's mother.
The Breast Lift of Champions
Now, of course there are different degrees of breast sagging, and some boobies may perk up a bit with the help of breast implants. However, the general rule of thumb is that if your nipples fall below the inframammary fold (the crease under the breast), then a breast lift or breast lift plus augmentation combo might be more appropriate.
You won't get any actual "lift" from an implant alone in the sense that your nipples won't be positioned any higher. It is possible, though, that additional upper breast fullness could mitigate the appearance of sagging or mild loss of volume. But, if your sagging is severe, breast implants alone will do nothing to improve the appearance of your breasts, and may only succeed in making matters worse.
Your plastic surgeon will help you to make sure you're getting breast implants for the right reasons—that is, to increase volume, not change breast position—and recommend the breast enhancement procedure that's most likely to help you meet your appearance goals.