Before we had the DHF there pretty much was no use for HBD beyond speculation. The DHF doesn't need HBD to function, DHF could just payout in Hive instead.

There's really no use case for HBD as you can already use DAI for almost 0 fees by using sidechains, and when Ethereum starts rolling out all the huge updates they are doing to turn into POS there will be virtually no fees on layer 1.