Hi,
Here is the explanation from the workflow help page.
"Changing the master contract triggers a workflow that accesses the assigned lower level contracts and automatically copies the changes to the lower level contract. If an error occurs, a work item appears in the inbox of the person who changed the master contract, who has to process it manually. A separate window displays all the changes that have been made for information purposes."
More info here Change Master Contract (SD-SLS-OA) - Sales and Distribution (SD) Workflow Scenarios - SAP Library
Regards,
Thanes