IEstimate.NeedsRecalculateCosts Property
The method uses multiple criteria. It first checks several global re-calculation flags. If these are false, then it checks whether there are some minute rows marked as not up to date or if their embedded workbook needs calculation.
A situation when the minutes rows might need to be recalculated occurs, for example, when a user sheet is edited in the overhead. Such changes in an overhead sheet might affect global variables or coefficients. Moreover, an embedded workbook might use dependent values from overhead.
It's hard, if not impossible, to detect such situation accurately for 100%. That's why this values indicates only that the minutes rows might need to be recalculated. If the value is true, it's still possible that no minute row needs any recalculation. But if the value is false, you can be sure that no recalculation is needed.