Achieving Economies of Scale
Two or more producers can benefit from joining together to build a single facility when there are economies of scale in production. For example, two aluminum producers might decide to build a single aluminum processing plant near a location where each has a large supply of bauxite.
Or, the firms in a densely industrialized area might decide to cooperate in a single cogeneration facility, with each firm agreeing to buy steam to meet its own needs for heat and the group selling all the excess electricity to the local electric utility.