Journaling is a function that is only valuable on the system startup drive. Journaling in UNIX, is a defeatable function (on-off) that saves a running log file of the condition of the running processes and their data on the system drives. This is only valuable when the system crashes or one of the processes running exits permaturely. When the system starts up again after a "hang-crash" situation, UNIX can access this log files and deal with the improperly exited processes. Without Journaling, the startup would take the time to verify the intergrity or each mounted volume and all the processes that were in memory, last runtime.
Journaling essentially, save you startup time.
You do NOT need to turn Journaling on on the Firewire drive, and it is best to initialize it on your computer before using it.