Import option - Insert new & keep existing

Can anybody explain the difference between "Insert New" & keep Existing in the import option.

Following is the explanation in help.

Keep Existing: Retains data in the existing project and does not overwrite them with the updated data; adds new data if the record does not exist.


Insert New: Retains data in the existing project and adds any new data items.

To me both are the same as per the explanation nin the help.

I would like to know if anybody can crack the code.

thanks,

Rajeev