There are several reasons I've kept a journal:
+ Writing is thinking.
+ I believe it makes my writing better, even if only via the additional practice.
+ Journaling has been, at times, a sanity check. Writing about some craziness in my life provides a way to stop ruminating over it.
+ Journaling is a great way to explore ideas that I have.
Over the past three months or so. I've focused more on journaling as a writing and exploration tool and much less as a safety valve over observations of meanness or stupidity in the world or some sadness I might experience. Those things are easy to write passionately about, however I'm generating enough ideas I feel passionate about that I don't need to tap that resource.