I told both of my Ts lots about what I consider my darkest secrets - my self-destructive behaviors, addiction and what came with it especially. I did not find it all that useful though, much more helpful for me to discuss these with peers that experienced similar things and resolved them. Deepest for me are things that I still feel most insecure and/or ashamed about, and I did discuss some of that as well but far from all or even closely comprehensive. Those are things I much prefer to talk about with friends.