Hopefully someone can answer this more eloquently than me.
But from what I've pieced together, the forecast assumes all resources (agents) in the planning group are valid/selectable for routing when figuring out the resources required per interval.
Preferred agent breaks this modal, since by it's nature not all resources are available for routing interactions, so it is going to inaccurately predict the resource requirements per interval and by extension the expected aht, asa etc.
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Anton Vroon
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