It limits journalling of messages forwarded to a forwarding address specified in a person document.
Setting JournalLimitForwardToMailAddress=1 will prevent this duplicate copy of the forwarded message from being journaled. The original message will still be journaled. This setting must be enabled on the server which has journaling enabled, and which is doing the forwarding.
Recommendation: Enable this option on servers with journalling enabled because it can substantially reduce the size of the journalling database.
Domino Configuration Tuner: This setting is included in the DCT catalog of best practices as of Domino 8.5