Waiting list
When an event sells out the form becomes a queue, and places that free up are offered in order, one at a time.
A sold-out event is a page that still has people on it. The waiting list is what you do with them.
The form becomes a queue
When the last place goes, the booking form turns into a waiting list form. The visitor leaves their name, how many places they want, and which ticket type. They keep a position in the queue.
One offer per place
Somebody cancels and the place is offered to the first person who can use it, by a private link, and to nobody else. Two people are never sent the same seat, which is the mistake that turns a good gesture into an argument.
Offers expire
An offer holds the place for as long as you allow and then moves on to the next person. A queue that stalls because one person is not reading their email is not a queue.
A claim is an ordinary booking
Following the link makes a real booking: same form, same payment, same ticket, same confirmation. Nothing about it is a special case afterwards.
The list can be turned off for the events where it does not fit.
More in Waiting list
What happens after the last place has gone.