Understand User Request Status field

Summary:

We want to understand what "user request status" field in fulfilment line means and why it is blank for some lines in a Sales Order and Completed for some lines even though line status are same. I have a sales order with 10 or above lines. There are lines with status "Awaiting Shipping" and user request status as completed and line with same status but user request type as Blank. I have a different warehouse management which ships order line. There are cloud to this application integration both Outbound to provide Order details and inbound to get line status details.