While with enough refinements VB and MO theory in the end converge to the same energy value, a great advantage of VB is that it can clearly define in conceptual and mathematical manner our most basal ideas of the bond in chemical terms, such as the bond order, resonance, covalent, and ionic characters. Therefore, if we qualitatively consider the chemical bond as shared electron pairs (or in Lewis' words: "…to express this idea of chemical union in symbols I would suggest the use of a colon… to represent the two electrons which act as the connecting links between the two atoms" ), valence bond theory provides its quantitative quantum mechanical justification. While VB computations are harder than in MO theory, VB competes head-to-head in terms of explanatory and predictive power. Still, even if high-level VB can compute weak interactions, it does not have any kind of van der Waals structure. In these cases, like with orbitals, we cannot say that shared electron pairs make the bonds when there are no pairs in these bonds. Nothing is perfect, but quoting Voltaire, "the best is the enemy of good". And both VB and MO models are really good.