Ubuntu's implementation will also allow you to export a backup passphrase in case the TPM gets zapped (by a firmware update for example) after which you can re-enroll.

Annoyingly, this is a random 16 byte value that's translated into a numeric string that only Ubuntus's cryptsetup wrapper seems to use. You need to convert it into an actual key if you want to re-enroll your TPM or add a key file/passphrase to another slot.

If you don't back up the recovery key, your data is lost.