Hi,
controlling area is high node in controlling after opertaing concern. it controll all the cost related actives i.e. internal oreder,commitment,project systems e.t.c.. one conrolling area can used for multiple company codes for this reason when we create controlling area if you select cross company code it will all you cross-company transaction if you use same conrtolling area for multiple company codes COA should be same for all company codes.
company code is high node in financial a/c without this nothing will happen. it's legal entity.
I hope it's help.
come back if you have queries.
Regards,
Raman