What happens when someone has a reduction

Do they recycle the reduced part and use it for implants or enlargements?(You know, for ...those... type of reductions) I just want to know for knowledge's sake. Also because I'd find that better than using plactic or something of the kind. ^u^

have you ever read in the context of organ donation that the tissue of the donor and the recipient have to be matched or the body of the recipient will reject the tissue as foreign? Even then the recipient frequently need to take immune suppressants for the rest of their life.

I don't think that's something even the most crazy person who wants a breast enlargement wants. There are only risks, there isn't really any benefit.

I would expect that "leftovers" are treated as biohazardous material and incinerated, though I can't claim to have any real knowledge.

I assume you are talking about breast or butt reductions. Stop me if I'm wrong . . .
Most of what is removed is . . . you guessed it . . . fat!
So it would not really be suitable to keep it around and then inject it into someone else who doesn't have enough . . .

I assume you mean breast fat. And it's exactly what that is, fat. Since it's made primarilly of lipids, it can't be used anywhere else on the body. So I assume they trash it.