I was told, when my cousin needed a bone graft, that they were better off using a piece of bone from a matching donor, rather than from another part of her body. Apparently it can take a long time to heal, and the body is having enough stress as it is, so they don't do autografts as often as you might expect.
Even though it is more ideal to use an exact match, and the only way to get an exact match without using your own bone, is to have an identical twin. But, other things need to be taken into account I guess.
It turned out she found a donor, so that was good, although the family did turn out to try and see if any of them were a good match.