This is a convenience function that reduces the content of the Argument to a numeric value by summing all the values for all metrics or KPIs in the Argument. It is most applicable when a single KPI or metric is input to the KPI formula as it provides a shorthand way of processing the single input. For example 

//reduce the input to the latest value
metrics = metrics.latest();

return {
 value :  metrics.value(),
 breakdown :  metrics.breakdown()
};

If the above formula is applied to a single metric input the output would be the same as the default behaviour for all KPIs that do not have a custom KPI formula.

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