When you create a custom KPI the 'aggregation type' determines how targets and non-financial KPI results roll-up to quarterly and annual periods.
For example, for monthly targets and non-financial KPI results:
Average: The quarterly and yearly results are the average of the non-financial results or target values for the period
Sum: Adds up all of the non-financial results or target values for the period
Balance: Chooses the last month's target or non-financial result, as the value for the quarter or year
For KPIs that include financial and non-financial variables, each variable will be aggregated according to:
Non-financial KPI results: Will be aggregated according to the aggregation type selected for the non-financial KPI.
P&L Results: Profit & Loss, or Income Statement, KPIs are summed for the quarterly or yearly results.
Balance Sheet Results: Quarterly and yearly results for Balance Sheet KPIs are determined by the ending balance for the KPI.