Some people are afraid of having implants and this an important thing to consider. I usually use implants to volumize the face when a person does not have a lot of fat to use, for example in women that are physically fit and have little body fat.
After implantation, you can then use the little fat that the person has to augment the implant. I usually do this in two phases with the implant first and then fat grafting at a later date. You also have to consider that fat and implants have different characteristics as well.
Implants require more incisions and usually are placed through the mouth. Fat transfer requires small holes instead of long incisions. Implants can also help in that fat transfering is needed less and cuts down on the need for more extensive fat harvesting.