Size, once past certain threshold values, may or may not matter during sex, there are too many interrelated variables to tease out a definitive statement.
However, size definitely matters in the ability of organizations to bear and spread risk. Insurance companies when they are operating in a manner that benefits the public are supposed to be experts at identifying and spreading risk throughout a population. The larger the population where risk can be spread, the closer the spread distribution of risk is to the absolute risk inherent in the population. The less variance between the risk pool and the aggregate risk, the cheaper the cost of covering and insuring against that risk becomes.
Obamacare has encouraged a trend that exisisted before 2009, and that is provider consolidation.