You can define source list validities in SAP R/3 for external procurement relationships (scheduling agreements, purchasing info records, contracts). By default the information for the source list records is not transferred to SAP APO. SAP APO creates a transportation lane for each external procurement relationship, without taking the source list into account.
If you set this indicator, SAP R/3 transfers the information from source list records that are marked in the source list as MRP-relevant to SAP APO. All source list records for which 1 or 2 is entered in the column Source List Usage in Materials Planning in the source list are considered to be MRP-relevant. Source list records for supplying plants and blocked source list records are not transferred. SAP APO creates a transportation lane for each source list record transferred.