If you write for the public, if you are a novelist, screenwriter, blogger, etc., your journals might be a source of inspiration. You might be able to harvest from them.
Let’s say you are a Young Adult novelist. Could your diaries from the age range of your reader help to get you into the mindset of your characters? Could some of the problems of youth become the main conflict for your protagonist? Would reading your older diaries at least get you in the mood for writing for this age range?
How can your private journals help you to write for the public?