True, but then what about connecting passengers? To get around that on a tough flight to make, I could fly PHL-SCE, then check in at SCE for SCE-PHL-ORD if the PHL-ORD route was full.
Well, no. Not under the AA system. The non-rev travel system does not allow a booking of PHL-SCE-PHL-anywhere
on the same PNR. Otherwise, DFW would be a total mess because of the destinations within 1 hour of DFW, such as AUS, SAT, OKC, etc. When you add in the AE destinations from DFW it would become even a greater nightmare.
If you book DFW-AUS, you can come back the same day and go on to another destination, but not on the same PNR. And, if you have a different PNR, then you will have a different 24-hr check-in time for the 2nd PNR--i.e., you would not be a through passenger on the continuing flight on return from AUS. And, no you cannot do a one-way to AUS with the AUS-DFW-somewhere else on the other PNR. If you originate at DFW, you have to come back to DFW on the same PNR if same day. There are safeguards in the programming to prevent such gaming of the system. For instance, once you check-in as a D2 (the most common travel status for employees). If you then find out that you are low on the standby list because other people get up earlier and check themselves in at the first opportunity, you can not delete your PNR, then re-list as a D1 to put yourself higher on the list. The system will flag the whole transaction.
And, considering how rapidly the # of available seats can change, do you really want to risk getting to AUS, but not getting back in time to catch your flight to LHR, or not getting back at all? If you don't get on the flight, wouldn't you rather be at "home base" when you find out you ain't goin' today?