Purchase Orders in Material Workbench

Can someone tell me the intended purpose for the Purchase Orders section of the Material Workbench (Onhand Availability)?

So If I query an item and I select the Inbound checkbox, in the results there is now an Inbound section which includes Purchase Orders, Internal Requisitions, ASNs, etc.  We never see anything under Purchase Orders if we expand it.  When should we be seeing information there? I've tried searching documentation but haven't been able to find any specifics so if anyone had some that would be great as well. We are on 12.1.3.

thanks,
Janel