It is true that many tables show several archiving objects in DB15, but that does not necessarily mean that you can use them alternatively.
CO internal orders, production orders and process orders for example are all using the table AUFK, but you cannot archive internal orders with the object PP_ORDER, you would need to use CO_ORDER for internal orders. Each of those objects archives only their individual part from AUFK table.
The same happens with purchase requisitions that are stored in table EBAN, here you see archiving objects MM_EBAN, PP_ORDER etc.
MM_EBAN will archive the the neutral requistions, requisitions that have no specific order relation, while PP_ORDER includes the requisitions with order relation.
Coming back to the CO tables, if you archive the CO items independently then you will not be able to see those details from an archived sales order. You are breaking the direct relation.
It might be a quick win with table space, but a bigger effort for the users if they have to investigate CO item details from an archived sales order.
Same issue with archiving of change history. Not everything what is technically possible does make sense from a business point of view.