If free: can be used for research, doesn't just freeze up somewhere for years. There's a really slim chance it can help someone in need (very slim, though). If not free: some random company is feeding itself on your sense of insecurity.
Sorry, I should have prefaced it by saying that these are my opinions only for commercial ventures. If it's a govt. run thing for use by any needy person, I'd be all for it. Sadly such a set up did not exist where I live.
Cord blood banking seems to be a scam. I considered it briefly for our kid, but reading quite a bit about it, decided not to do it. Here's why: 1. Stem cells similar to those present in cord blood are easily obtained from our own (adult) blood if/when the need arises. 2. Very low chance that they will be useful to siblings/parents/other relatives. 3. No guarantee of how well these cells survive in the cryogenic environment. No guarantee from the banks of backup plans in case of failure. 4. All fancy stuff (about regenerating organs) from the cells is science fiction so far. 5. Medical science could find alternative ways to cure your conditions by then. 6. The bank guys are great at emotional blackmail --- like giving the greatest gift to your newborn, and being a bad parent otherwise. I had one guy who told me that I might even make money selling it in future. Shame on him.