I wonder about this too because I want to tell my T everything I'm feeling and thinking about her and about the therapy relationship. Then there's physical stuff. She would always ask where in your body do you feel something, so I tentatively started talking about things I thought were TMI. For me, I need to know that nothing is off-limits because I feel so much shame about myself.
I don't tell her what I had for breakfast every day or everything I do, but she knows a lot about my daily life also. She says nothing is TMI and I've tested her on that, so I know she means it!

I think the only time you can share too much is if it's non-relevant information that is keeping you from doing the real work of therapy, like talking about your job all the time, or about your pets, or something like that. But I don't think that's the kind of sharing you're talking about, is it?