My son just got a stem cell transplant, so while I am not familiar with the other uses of cord blood, I am familiar with transplant and needing a stem cell donor. My son got a marrow transplant from an unrelated donor off the bone marrow registry. His brother was not a match.
Some thoughts
1) Keep in mind that if your child has cancer or a blood disorder, they would not use the banked cord blood to transplant back into him as your child's blood and marrow will be considered "defective" (for lack of a better term). What the cord blood could be used for is a sibling who needs a transplant.
2) From what I understand from my online support groups of cancer moms, cord blood in some ways is better for a transplant than marrow b/c there are less issues with immune incompatibility. Meaning, if your child A needs a transplant due to a blood disorder or cancer, and Child B is a match - they may use the cord blood of child B instead of marrow. I may be wrong on this. It is free for people with a child with cancer to bank the cord blood of their siblings for this reason (I think a non-profit does it?)
3) The other issue with cord blood banking is that there is not much volume of cord blood. My son is 14 and the size of an adult. If he were to have a cord blood donation, we were told it would be 2-3 different cords just to equal the volume of cells needed. Very young children can get by on 1 cord.
4) Siblings are only a match for transplant 30% of the time and typically no other relatives are considered for transplant. If there are no other good choices, sometimes a parent is used. It is a common misconception that the DNA of donor and recipient needs to be as similar as possible - only 1 part of 1 chromosome - the Human Leukocyte Antigens - need to be the same. My younger son (I have 2 boys) was the only relative tested.
5) Due to lack of volume of cells, lack of match, etc. we would not have been able to use our son's cords if they had been banked. I know a mom whose daughter needed a transplant and all 4 of her siblings were not matches.
6) The field of immunotherapy in blood cancers is exploding - CAR-T cell therapy being the most used. It is hoped that someday this therapy will dramatically reduce or eliminate the need for transplants in blood cancers. There are blood disorders - sickle cell, aplastic anemia, etc. that use transplants for treatment and immunotherapy would not cure.
7) All that being said, I have no idea about the other uses of cord blood and science changes all the time. I know that stem cell research would be huge for my son's cancer (leukemia).