So wouldn't that mean your best bet is if CLT-YYY was delayed? It wouldn't really matter if XXX-CLT was delayed since as has been said they're obligated to get you to YYY, so actually you're probably better off if XXX-CLT is not delayed since they could reroute you to YYY (unless XXX-CLT is very delayed and they can reroute you to YYY which even with the additional driving would still get you to your final destination sooner).

I've flown GSP-CLT-XXX to save money, and one time my GSP-CLT flight was delayed before I made it all the way to the airport (was about 5 mins away though), called and said I would drive back to CLT which they let me do (and then I probably skipped the final leg on the return trip but don't really remember).