Defintely not "To get the flight and crew home" - more to enable a flight that has, for unforseen reasons, gone out of schedule, to complete that flight, to scheduled destination, regardless, but subject to the crew being fit to do so.
The purpose of discretion has, at times, been abused. I have heard of people leaving base on a multi sector flight knowing discretion would be required to complete the schedule yet, at one time, the captain could only exercise discretion at the commencement of the final sector having properly assessed the physical state of all the crew members.
You will probably get a few more, different interpretations too!
