It is common for a BOM to have a wide variety of components/items associated in it (For Example Screws, Washers, Nuts, Hardware, Motors and sub-assemblies). Many would organize those components/items in more than one workspace within PLM360.
In order to mass create/update BOMs of a specific product practically, the import tool must allow access to add/remove 'child' items from other workspaces - Especially if PLM360 allows you to do it manually.
Having access to only the 'Parent' workspace in the import tool is impractical. This either results in poor item organization within the workspace when trying to make the import tool work OR results the user performing a tedious manual process.
Overall, I think the import tool is a great feature for BOMs; however it still needs to incorporate a multi-workspace functionality to serve its purpose practically.