I think that just like anything else, within moderation, a little bit of self disclosure could maybe help the clients (depending on the situation obviously).

My first T told me a fair amount of personal information, and it only made me feel closer to her. It showed me that she could emphathize with that i was saying ... made me feel less alone, and like she wasn't judging me. In my case at least, this helped me.

I can see however that if a T was to share such personal information such as his or her own current mental illness, or marital life ... imposing this on their client ... well then yes this could be seen as a negative thing.

It also depends on the relationship that the T has with their client too though. I know that if my other T's had told me such personal information i wouldn't of known what to do with it, or how to interpret it because our relationship wasn't nearly as developed.

Like i said ... i think it depends on each individual relationship - but was grateful for my T's self-disclosure.