How do you determine when to use your own bone marrow vs. a donor?

The selection of the type of transplant, autologous (from one's own cells) versus allogeneic (from a donor) depends on multiple factors. We always take into account the primary blood disorder, the involvement of the bone marrow by the disease, the patients overall health and donor availability prior making a final determination.
You can have more than one transplant and under certain circumstances this might be planed from the beginning (like on patients with myeloma). You might also have a second transplant if you have significant benefits from the first one, like a very long remission and if you remain in good health.