An element must be set as an output element in Live Price Grid when:
It is referred in the api.currentItemByElementName() or api.getPropertyByElementName call as a parameter. This function is used to find the value before the calculation, so in order to keep that information, the item must be visible.
It is marked as 'Allow override' (therefore it is referred in the api.getManualOverride() call as a parameter). The approach is clear: if I should be able to override a value, I need to have a field where I can write this value to.
The critical alert can be set in that element both in the UI or via api.criticalAlert(). For api.redAlert and api.yellowAlert this is not the case, since if they don't want to see the value of the element at all, then it does not matter if it can be red or yellow.
It it is referred in an alert comparison condition in another element.
It is a KPI to be referred to in approval workflow conditions (i.e. “ForcastTurnover”).
It is a field that the users use for filtering/sorting for (i.e. “ProductGroup”). (However, parametrization of pricing strategies would also work without having this in visible output fields.)
It is a field that the users need for filtering / drilling down / using in the LPG/PL summary to evaluate the quality of the overall price adjustments of a price list.