Why are there high variation rates in procedures?

The Atlas of variations in health care describes what's going on in the real world. Once we know that there are large differences in hospitalization rates between geographic areas, we need to ask about the causes behind them. This is much more complicated.
Have a look at this article and you'll become convinced that it is possible to reduce potential inappropriate care, and hence reduce costs, without harming health. A key paragraph:

Si un área tuviese el comportamiento de las áreas con tasa en el percentil 25 como referencia, el exceso de coste anual oscilaría entre los 89 millones de euros en el caso de proctología hasta los 12 millones en el caso de revisión de artroplastia. En el caso de usar como umbral deseable la tasa del percentil 5, el exceso oscilaría entre los 22 millones atribuibles a revisiones de artroplastia y los 129 millones a procedimientos proctológicos.

This is a clear message for those at the helm of  budget cuts. It's the kind of message that a politician wants to avoid tackling. Anyway, handle with care, this is only a description. There is no clue about causes and consequences.