Group BOM ↔ Plant-Specific BOM
You can create a BOM without reference to a plant in the form of a group BOM. This is useful when an engineer is working with a BOM during the engineering phase, but does not know yet which plant it is used in. The group BOM can later be converted to a production-relevant, plant-specific BOM. To do this, you can either assign a plant or create a copy of the BOM.

To assign a plant, you simply add a plant to the group BOM. However, it is still the same BOM, with one internal BOM number. Therefore, when a group BOM is changed you see the changes in the plant-specific BOM.
A BOM copy is a second, separate BOM with a different internal BOM number. The group BOM only serves as a copy template.
You can select any direction for both plant assignments and copies.