I was duplicating an opportunity after it had closed and slected the duplicate all fields.
Interesting is that the contacts do not duplicate over.
It is rare that the contacts involved with an opportunity would not be the same ones with the new opportunity, especially when it is a renewal.
I can see that an opportunity with customer A may then be the same opportunity with customer B and the contacts would be different. In those cases, I have no problem removing the names and adding new names, but I bet the manufacturer's contact would be the same.