I always thought 'discretion' was originally created so that a crew, finding itself down route and with insufficient duty time to return home without breaching FTL's, could elect to continue as long as they all felt ok to do the last sector (to get HOME). In other words it's for the benefit of crew, and for the sole purpose of allowing them to legally do the LAST sector despite the FTL's. Or have i got it wrong (again!).