I do keep journals. While I destroyed my very first ones after the injury because I couldn't bear to read about the pain I was in... I have journaled for years since. I have boxes and boxes of them sigh. I live alone or the idea of someone reading would drive me ahhem..crazy? After I'm gone, then let whomever read them! If they never knew the pain I was in, that was their doing, not mine.
My journals have come in handy, as my memory continues to fail. I insist my T had said such and such and when I review it in session and he disagrees as to his stance, I dig out the journal (yes it might take a few days to find the right one) and read ...that the T is remembering correctly. Without my noting in the journal, and then reading it, I would always question.
It's best to make them so you can reread, and see where you progress... but you are right, imo, that just the writing it out can be therapeutic.

TC