I've seen many places explain the dipole moment of ozone from the formal charges of the O atoms. However, I don't quite feel comfortable with this explanation since I feel like formal charges are not actual charges; they're more like a bookkeeping convention.
From this question, it seems like we should take into account the lone pair on the central O when summing the dipole moments. Thus, shouldn't the central O be the negative end of the dipole (since it has the lone pair)? But why does this contradict the prediction made by formal charges?
In general, to find the overall polarity of a molecule, when is it appropriate to sum up all the dipole moments (including those from the lone pairs), and when should we use formal charge instead?