Value in mergers?

Where do the value in mergers come from? Here's a paper that has a crack at answering it.

We estimate that tax savings contribute only 1.64% in additional value, while operating synergies account for the remaining 8.38%. Operating synergies are higher in focused mergers, while tax savings constitute a large fraction of the gains in diversifying mergers. The operating synergies are generated primarily by cutbacks in investment expenditures rather than increased operating profits. Overall, the evidence suggests that mergers generate gains by improving resource allocation rather than by reducing tax payments or increasing the market power of the combined firm.