Dangers of fat transfer? How common are the risks like embolisms?

I appreciate your concerns, however facial fat grafting is very safe. There are risks of fat embolism in procedures like BBL when a large amount of fat is transferred to the buttocks. There is significantly less chance of this happening with facial fat grafting. Consult with a board-certified plastic surgeon in your area to confirm my advice. Good luck.

In reality the biggest danger of facial fat transfer is undesirable aesthetic outcomes leading patients to regret having the procedure and having further procedures to correct the results.
Serious medical complications are pretty rare with this procedure.
I don’t know if anyone has ever described a venous fat embolization during facial fat transfer. If it has happened I can assure you it’s pretty rare.
This has been reported with gluteal fat transfer but only for that anatomic seizure.
Arterial embolization‘s have been reported with the use of fillers when sharp needles are used in this can lead to areas of facial necrosis. The chance of an arterial embolization is exceedingly rare when needles are not used.
Other potential injuries include facial nerve damage which is almost always temporary.
Injuries the structures like the parotid gland can happen but are also pretty esoteric and unlikely.
Some patients will bleed to the point of being bruised for several weeks after the procedure. Whether this is a complication or simply an undesirable outcome or side effect is up for debate.
I suppose a careless provider could puncture the abdomen during the harvest effect. This is certainly been described from Liposuction in general.
Puncture of internal organs including the colon cancer and has led to fatal outcomes.
The list of what can go wrong can go on and on including loss of vision, stroke etc. etc.
If you focus on the worst case scenarios no one would ever have any procedures.
Risk needs to always be assessed in relative terms to frequency.
People are often willing to drive or ride in motor vehicles despite being one of the most dangerous activities people do.
Fatality rates for driving one year is far higher than having a typical surgical procedure.
Facial fat transfer has a fairly high chance of having outcomes that are different than what patients had anticipated.
The procedure by its very nature is fickle, unpredictable and to some degree is a bit imprecise in comparison with fillers. 
Extremely talented experienced providers have a far better chance of delivering consistent high patient satisfaction without problems.
I do not consider facial fat transfer as being higher or even moderate risk in regards to life-threatening complications.
I don’t have statistical numbers but my best guess is a serious medical complication for this procedure is probably around 1:15,000. A moderate complication like forming a blood clot or temporary facial nerve injury is going to be much more likely. these risks may be as high as 1:500.
Undesirable outcomes obviously very on the degree but I would say probably 20% of patients at least have some issue with the results. Probably more than that.
Patient posting on real self asking how previously grafted fat in the face can be removed is not uncommon.
Personally I find fillers to be far superior and recommend staying with those.
The temptation of thinking fat transfer is far superior is easy to understand.
In assessing risk benefit ratio‘s risk is only 1/2 of the equation.
The benefit part of the equation needs to be considered as well.
This starts by determining if someone is a good candidate for a procedure.
People who are exceptionally good candidates for certain cosmetic surgical procedures probably should be willing to take increased risk because the procedure can have a profound a positive influence on quality-of-life.
Those who are mediocre or not particularly good candidates unless justified in taking any risks.
I suggest scheduling multiple in person consultations with local board-certified plastic surgeons who have a proven track record with this procedure.
Best, 
Mats Hagstrom, MD

Like anything else, the safety and results of fat grafting are dependent on the injector. Fat transfer is, in expert hands, very safe and has excellent results. make sure the plastic surgeon you see is an experienced expert.