Its really a difference between scoping to a specific database mailboxes ( standard) and being able to scope to recipients (Premium)
Premium requires Enterprise CALs.
https://learn.microsoft.com/en-us/exchange/policy-and-compliance/journaling/journaling-procedures?view=exchserver-2019
You wouldnt enable both simply because if you have Enterprise CALs, then use Premium, if not enable per database with Standard.
If both were enabled, you may see some duplication in the journaling maibox.