One problem is the unknown blood transmitted illness (something like AIDS, or Hepatitis C, some years ago before the blood tests were common). In the normal case, you are in an ER and your options are dying now or a blood transfusion with a low probability of an unknown illness. In this case, you are trying to live for a looong time, and receive a lot of transfusions. Each transfusion increase the probability of a problem, and the possibility that your life expectancy is reduced.
One problem is the unknown blood transmitted illness (something like AIDS, or Hepatitis C, some years ago before the blood tests were common). In the normal case, you are in an ER and your options are dying now or a blood transfusion with a low probability of an unknown illness. In this case, you are trying to live for a looong time, and receive a lot of transfusions. Each transfusion increase the probability of a problem, and the possibility that your life expectancy is reduced.