They will usually announce that they are overbooked and ask over the local section intercom if anyone is willing to take the next flight. You can actually get cash out of it if nobody else wants to go later, sometimes more than you paid for your ticket. Plus a free ticket for the next flight.
If you’re not lined up (or late) and the plane is already full, then they can’t seat you and you’ll have to take a later flight by default.
They will usually announce that they are overbooked and ask over the local section intercom if anyone is willing to take the next flight. You can actually get cash out of it if nobody else wants to go later, sometimes more than you paid for your ticket. Plus a free ticket for the next flight.
If you’re not lined up (or late) and the plane is already full, then they can’t seat you and you’ll have to take a later flight by default.
https://wanderwisdom.com/transportation/why-do-airlines-always-overbook-their-flight