Say we have an HCl molecule. The difference in electronegativities of the H and Cl atoms tells us how polar the HCl molecule is. The dipole moment is also a measure of the degree of polarity in molecules.
So why do we need the "dipole moment" concept if we can see how polar a molecule is by looking at the electronegativities of the atoms in the molecule? Is it because in complex molecules it is easier to measure how polar a molecule is, using the dipole moment formula?