That just means the TPM will not auto unlock the encrypted disk. You would have to unlock with whatever LUKS password (or key file) you set for that drive. There is optionally a TPM master key you can export that similar to the Microsoft Bitlocker password (40 digit number iirc), that Lennart mentioned in his blog. If you deleted any other pass slots and do not have that TPM master key, you will not be able to unlock the LUKS drive.
If you look at that freedesktop manpage I linked, it states some of the PCR values and what each one measures. When you enroll a PCR, that value is stored in the TPM. If anything differs between the system and the TPM, the TPM will refuse to unlock that encrypted drive.
For example, PCR 0 measures your mother UEFI firmware. If you update the firmware, the TPM will not unlock your LUKS drive until you re-enroll the drive once again. Is is a personal choice, but enrolling certain PCR into the TPM can be more inconvenient.