There is some overlap with PSA set registry, but there’s a few added benefits I can think of.
1.) Permanence - The blockchain would be a permanent registry that would exist even if the grading company disappeared and shut down.
2.) Enhanced Verifiable Authenticity - If you buying an NFT issued graded card, then you would naturally have the NFT sold along with the card. This would eliminate the risk of buying a fake graded card or at least greatly reduce it.
Because if even if someone could produce or replicate a fake graded slabs, they could not produce the NFT associated with the Cert# as it could only be issued by the grading company and anyone could verify it.
3.) Detailed Providence - Every time the card changed hands with the NFT it would be recorded on the blockchain. So you could literally see the recorded history of the lineage of very owner of the card. We can’t really do that today. For example if you bought a card from someone notable or famous. I am sure there’ll be people would value that information and have it verifiable. To be able to say, this card was previously own by King Pokemon, Logan Paul or whoever. Some people would quite possibly even pay a premium for it.