I've always liked journaling ever since I was little. But when I was a teenager my mom snooped in my room and read my journal which had very private things in it, and I've been super paranoid about writing serious and private things down on paper ever since.
However I do write in an online journal (penzu.com) and have for about five years. I write immediately after each therapy appointment about what happened, what we talked about, and how I felt about it because I have a terrible memory and it helped both to remind me before my next session, and also to look back and track my mood. I write in between sessions too, or I'll write things down to remind myself to tell my T.
I never showed my T or told her, I just used it as a tool for myself.