One thing that I feel is important about writing is that every time you write you make yourself more of the person that you want yourself to be. That's not always great if you're in terrible shape, but generally being motivated to write is a sign that there's something alright there that should be fostered (rare exceptions like Sylvia Plath aside).

I've certainly done my fair share of writing for an audience of myself, and while I don't know that I want to make a habit of it (outside the realm of practicing and self-assessing so that I avoid certain mistakes in my other writing), it's something that has helped me.