Like most of the other posters, we do get some sort of a release. It's a way to change the inner pain that you really can't do anything about and change it into a controllable pain: physical pain. This helps control some of us from doing worse things i.e. for me would be suicide. Self punishment too.

But most of all... when the scar is on its way to healing, I get this sense of satisfaction every time I take care of my scar. I would think that with this, I am taking care of myself.. a way that I am not able to take care of myself emotionally.

However, with that said, like what others have posted... please please do not start it. It's a horrible addiction that leaves permanent marks.