Quoting Chroma Hex [+1]:" I'm the same way. I would rather not get emotionally attached. But a friend of mine thinks that getting ... [snip!] ... that getting to know a person could stop a guy from being scared off by something he would have been worried about initially. "
That would be my reasoning. Not only just for me, but for him as well. I am manic-depressive (or was, who knows, I have not had a depressive period since I moved out of my abusive step-mom's house almost 6 yrs ago) and I still warned my now husband about it. I was honest, and said what happens, but that it was something that does not effect me often. He was fine with it.
I had a teacher once tell the class (adult class) that it important to disclose those things just incase something comes up in the future. Just so that the person is aware it can happen and so they wont freak out when it does happen.