The WFTC-38 added functionality of persistent transactional records which are stored when the outflowed transaction is prepared as the XA resource. Currently the persistent storage is a file system (for WFLY it's by default standalone/data/ejb-xa-recovery/).

In case the transaction manager (e.g. Narayana) stores data in a database (with JDBC) then the user should have a chance to define that the outflowed transactions are stored along with them. This is especially important for environments where file system storage is not available and the JDBC database is one of the few options.
This objection is relevant especially in cloud deployments especially.

In case of WFTC being deployed in WildFly, the storage should be aligned with the Narayana object store. When file system storage is used then WFTC uses that as well. If the Narayana object store uses JDBC then the WFTC should switch to JDBC as well.