What are some of the bad side effects of a Brazilian Butt Lift. And what is better, a BBL or Butt implants?

Allow, me to share
with you some information that you may not hear elsewhere. There are only two
proven safe and relatively effective methods for Buttock Augmentation and Hip
Augmentation: 1) Autologous Fat Transfer (using your own fat, transferring from
one area of the body to the other) and 2) Buttock/Hip Implants (semi-solid
silicone rubber implants that cannot rupture &/or leak). Both are very good
options so what it comes down to, like any surgery, is proper patient
selection. Depending upon the
amount of your current fat reserves and their distribution, you may or may not
be a reasonable candidate for fat transfer. Indeed because at least 50+ %
of the fat transferred will melt away within a year, most patients are not good
candidates because they lack an adequate amount of fat to harvest. Another tip
is that if you purposely gain weight (i.e. fat) for the procedure, the fat you
lose first as you get back to your baseline weight is that very same fat that
was transferred into your buttock...so don't fall victim to this
recommendation. Although using your own fat is relatively safe, the one
serious complication that can rarely (< 1%) happen is "fat
embolism" in which some of the fat gets into the blood stream and travels
up into the lungs, heart, and/or brain causing serious problems. This
complication is more likely to happen with the larger amount of fat being
transferred. This is even more likely to happen when using fillers like PMMA
and hyaluronic acids. Also fillers, when injected in large quantities, have a
relatively high tendency to migrate away from the original area they were
placed and tend to stimulate a lot of inflammation and a subsequent disastrous
amount of scar tissue/hardening.Thus buttock/hip
implants become a very good, safe, and long term reliable option for most
patients seeking buttock augmentation (at least in my practice). I prefer to
insert the buttock implants through a 2 inch long incision over the tailbone
(concealed within the crevice between the buttock cheeks) and the hip implants
through a ~ 1 inch incision just below the beltline above the hip region. The
buttock implant should always be placed under or within the gluteus maximus
muscle. In this position, the implant is less palpable, less visible, and does
not sag or shift/migrate over time unlike implants placed on top of the muscle.
Therefore it is extremely important to seek consultation with a board certified
plastic surgeon who specializes in this procedure (in fact both implants and
fat transfer so that s/he is not bias). And in this case too, at least in my
surgical practice, the infection rate is minimized to ~5% and the infection rate is minimized
to ~2%.
I generally do not recommend fat
grafting at the same time as placing buttock implant because of a
significantly increased risk of infection. For fat to survive it
must be grafted into muscle, however that is also where the implant sits.
Thus, if fat is injected into the implant or implant pocket then it will
die and almost assuredly get infected - necessitating removal of the implant as
well. Because
of this risk, I frequently avoid fat grafting into a buttock that has an
implantBecause of all this, I strongly recommend consulting
with a board certified plastic surgeon that performs both procedures and not just the
Brazilian buttock lift so that s/he can provide you with an unbiased
recommendation for surgery with realistic long term results.Again, like any surgery, the key to a
satisfactory outcome is both patient education and a skilled board certified
surgeon specialist.

The worst case senario would be overwhelming infection, multiple cysts, fat necrosis, and complete loss of all the grafts. In my opinion liposuction with that transfer is much better for gluteal augmentation than butt implants. 

Both procedures provide excellent results if performed on the "right" patients based on the underlying anatomies and goals.  Brazilian butt lift, because it uses the patient's fat derived from her own body (fat graft), has almost eradicated the risk of adverse reaction as no foreign implant is used.  However, she should have enough excess fat to create a noticeable amount of augmentation. Today's buttock augmentation favors fat graft because it provides more amount of contouring and more natural results.  Nevertheless, butt implant surgery remains useful since not everyone has enough excess fat. It is important to note that both procedures involve some risk of complication, which can be avoided or at least minimized by choosing a skilled board-certified plastic surgeon.  Do not go to a non-specialist as this will increase the odds of botched results.