If a flight is overbooked, airlines have individual protocols that determine which passengers get bumped.
Those who've bought the cheapest fares are among those most likely to be earthbound.
Late check-ins are susceptible, as are those who have not completed online check-in and been assigned a seat. Frequent flyers with elite status are unlikely to get offloaded, as are parents travelling with infants, unaccompanied minors and passengers with connecting flights.
In some countries, especially the US where airlines routinely overbook flights, being offloaded can be lucrative. Federal regulations stipulate that the airline must ask for volunteers, who might be offered a cash payment, typically $US200-$400, and reassignment to the next flight.
The real pay-off is for those who are involuntarily offloaded. Compensation can be as high as $US1300, depending on their ticket cost and the delay time.
The European Union has similar rules governing compensation for offloaded passengers.
If you're dumped from an overbooked flight in Australia there is no statutory compensation. If you are denied boarding involuntarily on a Virgin Australia flight you are entitled to a payment of denied boarding compensation under normal circumstances.
If that happens on a Qantas flight the airline will offer you a seat on the next available flight, or compensation if that is unacceptable.