Create Tickets in Registration form
Create tickets is a feature that apply to the case when one event has multi-sessions on the event day.
Different Time slot or Sessions can use Create Tickets for people to register.
More than one option for the event can turn on Create Tickets.
You can also set quota for different sessions:
Turn Off Create Tickets:
It applies to the case that there's only simply one event and without containing other sessions.
Then you can set quota for a whole event, but not individual sessions.