Is there any benefit from creating hardened child keys from unhardened parents?

Question

In the context of BIP32, is there any benefit from deriving a hardened key from an unhardened parent? E.g., m/0'/0/0'? Are there any examples of where such a key is being used?

Answer 1

No, there generally is no benefit to use hardened derivation following unhardened derivation. I'm also not aware of anyone using such a construction. However there are test vectors that do this since it is a supported operation, even if not useful

The purpose of unhardened derivation is to be able to derive further keys from it without needing the private key. However hardened derivation requires a private key in order to derive, and that defeats the purpose of using unhardened derivation in an earlier step.