The blood is usually only usable by a relative/sibling... almost never for the child who it came from so if this is your only child you're planning on, it may not be worth it to you.
I don't think that's quite true, 'Almost never' - can I ask where you heard this?
This is what I found:-
Helping your child through private blood cord banking may be an unconventional means to secure your child's future. In fact, there are groups that protest the morality and question the ethics behind this practice. However, nobody can deny the fact that blood cord banking can protect your child in the future in case he acquires a life-threatening disease. Not only is it beneficial for your child, the cord blood can also be compatible to some members of your family who can also get sick. There is a big probability that the blood cord is compatible with a sibling if another child in your family is faced with a deathly illness. There is actually a 1:4 chance of a stem cell match between siblings. Blood cord banking can help your child get treatment for the following life-threatening illnesses: lymphoma, leukemia, Hodgkin's disease, breast cancer, aplastic anemia, sickle cell anemia, hereditary or genetic conditions, blood diseases, various other cancers, various immune system disorders, lupus, and so on.[/QUOTE]
This site has tons and tons of helpful data.
https://parentsguidecordblood.org/content/usa/medical/oddsofuse.shtml?navid=36
The charts down in number 4 and 5 on this page show you how much less self-use of cord blood there is.
Its also one of the most unbiased resources I've found. Its definitely pro-banking but does say that the cost of private banking is a real concern and encourages public banking whenever possible. The actual companies who advertise private banking use what I feel are unfair emotional appeals and project the possible number of disease that may be treatable in the future etc and make it feel like you HAVE to do it or else you're putting your child's health at risk. They list diseases that they hope may someday be treatable by cord blood... and thats good to know if you have that disease in your family, but its not a fact yet that its treatable, you know?
I cannot remember where I read everything, but I did read/hear once that the majority of cases where cord blood is needed, it is not effective at treating the child who the cord blood came from possibly because the same issues are there and it may simply buy them some time but won't be as effective of a cure as a sibling match from a sibling who does not have the disease. Sorry, wish I could find that data.