It isn't like therapy where the patient does all the disclosing and the therapist mostly listens. You must be just as interested in the other person's feelings, problems and opinions as you are in expressing your views, emotions and needs. Thus, much of your self-disclosure consists of giving feedback to the other person. Because you value the relationship, you are naturally concerned about the effect your disclosures will have on your friend and on your relationship. You don't disclose everything, especially not hurtful, upsetting or useless feedback.
Constructive comments help people grow, reach out, feel good and try new things.
Critical, judgmental comments inhibit others. Without complete disclosure people can't know the real you. When we go to parties, I want you to spend some time with me, don't drink so much, and stop coming on to everyone. Don't act like you care if you really aren't very interested. Don't pretend to be a juicy plum when you are really a banana.