Originally Posted by
ursine1
I think that, if there is enough time for a return flight in between the others it wouldn't be necessary to actually book it.
I could see theories why it would be necessary: Such as a divorced parent being forced to fly with their children to an airport, dropping the kids off, flying back home, then needing to fly out the next day to pick them up (or take another trip for another reason). Or business reasons. Or who knows why. I'm sure these reasons are infrequent and time wasting (businesses do that often to their employees), but in theory if a return trip was booked, it demonstrates that both outgoing trips are valid.