I understand the utility of the key block itself, and of a hash of the key, but I don't know why additional information would be necessary, so I can't begin to guess the utility of an additional bit of information.
- What does it signify,
- where is it used, and
- (how) can it be determined given the public key block?
It tends to be mentioned tangentially and in passing, which leads to confusion since clearly spacewalk recognizes a difference between fingerprint and ID, while some GPG documentation put out by Fedora includes the phrase
For KEYNAME, substitute the key ID or fingerprint of your primary keypair,
which makes it seem as if the two share the same purpose; but that doesn't make sense because if that were the case why would you need both to begin with?