So my guess would be that and/or is a way of underlining the point that the or is to be understood in its inclusive sense rather than its exclusive sense. Sometimes you want to explicitly indicate “or more than one of the above”, and and/or does that.
I posted about this a while ago. In my original post I think I confused my exclusives and inclusives.
Anyway, one of the arguments I tried out on them was that no language has a lexical distinction between inclusive or and exlusive or. One of my bosses immediately responded, "English does, or is exclusive and and/or is inclusive." My response was that and/or isn't a word. We left it at that.But I thought to myself, I bet and/or ends up being just like or by taking on an exclusive meaning.
I was vindicated last night. I was sitting on the can reading What to Expect When You're Expecting (It's good bathroom literature!) when I came across the following in a recipe for oatmeal cookies on p. 94:
"add ground cinnamon and/or salt to taste (both optional) when you add the milk."
I was thinking or was inclusive and and/or was exclusive. My boss was thinking the other way around, but I wasn't paying attention. (Maybe that's why she's not my boss anymore.) Anyway, I now understand that and/or is inclusive, which I think is what the cookie recipe shows.