This flag is controlled automatically by the Relation Type. For Replace relationships only, refers to adding the demand for down-chain parts to the demand for up-chain parts when the down-chain part is no longer a planned part. This assures that future demand for the older down-chain parts will be handled by the up-chain parts. Parts that are flagged as having Alternates do not roll up demand, since they continue to be planned parts until burn off is complete.