GG Downstream mining setup - uses NOREGISTER

Why do we have to use NORIGISTER for GoldenGate Downstream mining setup?

The NOREGISTER attribute is required if the destination is a standby database that is not part of a Data Guard configuration. OGG downstream capture uses standby feature while without DG config, so uses NOREGISTER option. 

The REGISTER and the NOREGISTER attributes of the LOG_ARCHIVE_DEST_n parameter indicate if the location of the archived redo log file is to be recorded at the destination site.

GG Downstream mining setup for LOG_ARCHIVE_DEST_N:

ALTER SYSTEM SET LOG_ARCHIVE_DEST_5='SERVICE="JOORDS" ASYNC NOREGISTER REOPEN=10 
db_unique_name="JRDS" valid_for=(primary_role)';