Dr. Ott Young has done fat injections during my reconstructive surgeries to help fill out and flatten scars left from surgery as well as to help plump up areas of your breast so both breasts look more symmetrical.
For example, my left breast had an indented area even after the reconstruction that was due to all the radiation. In order to make it more symmetrical to my right breast, I had minor surgery last June where she took fat from my waist and injected it into the flattened area.
In short, Dr. Ott-Young's uses fat injections to tweak the results of your reconstruction surgery so your breasts will look more symmetrical and natural. There is absolutely no harm in it.
The good news is that wherever she takes the fat, you will most likely look slimmer in that area. Since it's your own tissue, you body will not regect it either.
Dr. Ott-Young did tell me that the fat she moves has the "memory" of where it came from. For instance, She used my belly fat to build back my right breast. (I do have an implant in that breast as well.) If I were to lose weight, the fat in that breast would go first since I always lose weight in my waist first.
I hope that answers your question.
P.S. Dr. Ott-Young is an amazing plastic surgeon. People can't believe what a great job she did on me. As I've said before, had I known the end result of how my breasts would look today, I wouldn't have sweated the reconstruction process like I did.