I never used a tripod, and I do mean never, until I started shooting large format (5x7 and 8x10 studio portraits). However once I got used to it, now I wouldn't shoot portraits without one. If your face is behind the camera you may feel like you're in touch with the subject, but I don't think you really are. Now the camera isn't between me and the subject, and the results are completely different because the subject is relating to another person, not a camera. Shooting less formally, "candid" type portraits, I think hiding behind the camera is a good thing, though, in that it doesn't draw the subject's attention to you and what you are doing. Years ago in news situations and in classrooms shooting educational stuff I discovered that if I never made eye contact with subjects they would completely ignore me and my camera, and things would move along as if I wasn't there. Eye contact changes everything in the interaction.