The Inclusive "Or"

I found it really fascinating in our class experience that the "Or" function can also include both ideas. for example PvQ could also be P and Q. Why exactly do we use that function and what sense does it really make? Obviously, it make's DeMorgan's make sense, but it seems like there must be an actual reason for the inclusion.

I'm pretty sure I read somewhere that the ancient Greek Stoics used the "Or" function in the exclusive, and it seems that modern English language conventions do the same. So, why the change?