The Brazilian Butt Lift is a great procedure because it transforms your entire body using your own fat. However the fat is a graft and needs time to be incorporated when you move it from the areas that we liposuctioned to the butt that is augmented.
Smoking has a detrimental affect on this because it causes vasoconstriction (shrinking and blockage) of blood vessels. Since the fat is a graft it needs this blood to survive. Patients want to keep as much of the fat as possible when undergoing the procedure and no question that smoking will decrease the amount of fat that survives after the procedure.
I have patient quit smoking completely for an entire month before having their Brazilian Butt Lift surgery here in Austin with me. This will optimize the amount of fat that will last after the transfer. Of note you cannot use nicotine patches prior to surgery either as the nicotine causes the same issues as smoking.
I hope this helps.