Very late to reply as I joined this group recently. Override position is very helpful if you want to show a different position of the component at the top level (higher level assemblies). At the subassembly level that component position remains same but at the higher level assemblies that component position can be changed. For example, if you have designed a OEM kit (containg two components) and other users are using it in their assemblies then they can change/reorient the components positions (of the OEM kit) in their assemblies. The OEM kit (sub-assembly) will not get altered. In some cases OEM kit may be read only for you and still using the overide the component position can be changed at the higher level assemblies. It is also called as Variable Component Positioning (VCP).
ya thnks i got some what as you told but can you explain in terms of giving attachment of model in step by step