The larger point is that companies that 'synergise' divisions see initial efficiencies. However, over time, without external forces, those efficiencies atrophy

The larger point is that companies that 'synergise' divisions see initial efficiencies. However, over time, without external forces, those efficiencies atrophy. By having two customers for a service, at least one of those external to the organisation, competitiveness is kept in focus.