For newbies, Journaling is similar to the TTS (Transaction Tracking System) that was originally created in the Netware File System back in 1998.
A simple explanation of this addition to a filesystem is that all writes are logged in a table and any incomplete writes to the disk (in the event of a crash); can be backed out and the File system will "roll back" to the last know good state. This is accomplished by various checks to the "Journal" that indicate which file I/O tasks were not flagged as complete at the time of power loss of system crash.
Sounds great !! Sign me up !... Well, all good things incur a price, Audio Volumes should have journaling turns OFF since it adds overhead to the system that is not desired. In fact, if you own a battery backup, you may want to turn it off all data volumes since this will speed up the system and your odds of a "Power Loss" go way down.
Also, in the real world, corrupted volumes that were journaled are harder to mount and repair than non-journaled ones in my experience. That is to say if the file system starts getting messed up (from a failing HD) the non-journaled volumes at least mount most of the time and data is retrievable.