Rebate is a mechanism by which alternatives to get monies back have been notified. At times they are simplar than the refund under rule 5. Also option of rebate on duty paid allows usage of old credits without link to the use for the exports.
For example, in case of rebate of duty paid on inputs, the amount is returned to the exporter who cleared final products while duty was actually paid by supplier of inputs. Similarly, in case of export through merchant exporter, duty paid by manufacturer, while rebate can be granted to merchant exporter.