The type of assembly is intended to influence the way an assembly is presented in a Multi-Level Bill of materials and how it is processed when the work order is allocated and issued.
In this image below you see a Multi Level BOM.
In this BOM you can see that Item 4 is an assembly. Items 5, 6, 7, 8 and 9 are shown indented at level 2 indicating that they are contained 'inside' item 4.
Items 10, 15 and 19 are also assemblies.
If you were to use this BOM to Issue materials for a work order then miniMrp would issue all components down through all levels of the BOM and the OnHand quantities of all of the components, not the sub assemblies, would be reduced/taken out of your inventory.
This might not be the behavior that you want. Perhaps some types of sub assembly are built on other work orders using miniMrp's 'Build for Stock' feature. You wouldn't want to issue materials for those assemblies again.
