How important is it know about your partner's past relationship(s)?

I look at it like this...Her past is her past, who she was with and why is of no concern to me. If she chooses to reveal details to me then she has a reason to and that is her choice. I personally chose to reveal mine to her (and give her as much information about each one as I could remember)...why? Because I didn't want there to be any secrets between us, and I didn't want the risk of something possibly coming back from my past that might cause problems in our relationship (I wanted her to have an awareness for just in case, though nothing ever happened and I really didn't think it would). But I don't pry into her past nor do I press for details, because I know she is as open and honest with me as I am with her. If she feels it something I should know then she will tell me...she always has. Our relationship/marriage is an open book and has been from the start (which is how we wanted it), but we also respect each other's right to privacy as well.