I dissociate a ton, but I never knew that was what I was doing until I got into therapy and my counselor pointed it out. Now I can see how often I do it, and looking back, I see how bad it was when I was younger. I thought numbness was normal!
As deli says, it is a short-term way to cope with something scary or overwhelming. I am often 'gone' before I ever realize I am scared. Long term, I find dissociation unhelpful because it keeps me from connecting with others, with myself. When I first learned about it, I was adamant about not trying to change it, and my T was okay with that. Now when I want to connect with him, but am scared to and dissociate, I find i it frustrating, even painful. So I'm working to change it. All in good time.
This is the question I ask myself when I'm dissociating: What I am afraid of right now?