I have not had the check in terminals offer earlier flights to be, but have asked (on an $85 SYD-MEL flight) and they said yes and moved me to an earlier flight.
As others have said I think it depends on how full later flights are, and if they think they need space on those later flights. I guess once the aircraft has departed, it's wasted space.
As others have said I think it depends on how full later flights are, and if they think they need space on those later flights. I guess once the aircraft has departed, it's wasted space.