Rerun is used when we use Checkpoint concept in Cobol.. This concept will be particularly useful when U r using a tape dataset and an abend occurs at which point in general, while restarting the job, the processed record will be processed again. In order to avoid that, we use checkpoint and while we restart we would have defined a dataset in JCL that will capturing the no., of records processed.. So while restarting.. U can fetch the No., of record processed so that U can directly start processing from the record lastly processed. So thus it saves time..
Think I might have confused.. If so without hesitation do write back..