I typically perform both of these procedures at the same time. I find this works well and most patients would rather have one operation rather than two. There are several situations where I do think it is in the best interest of the patient to have the procedures performed separately but these probably account for only a small percentage of cases.
The breastlift or mastopexy portion of the procedure is a breast reshaping operation. The nipple is raised and the breast is reshaped around this new nipple position and a more youthful shaped breast is created. The areola is usually reduced in diameter.
The breast augmentation portion of the procedure is used to provide primarily fullness in the upper portion of the breast, improved projection and to improve the overall shape of the breast. Typically when the two stage operation is completed there is a scar completely around the areola and there is a vertical scar from the lower part of the areolar to the breast fold. In some cases there is a scar in the fold as well.
In cases where there is considerable sagging of the breast or if the breast is already larger a two stage procedure may be best. I agree with having several consultations. Ask to see before and after photos as well. Thank you for your question and best of luck.