An event ticket guarantees you have a "seat at the table", it gives the bearer access to the specific event for which the ticket was obtained.
With that said, a few events do not have tickets, like the annual costume parade or the destruction of Cardhalla, for example. These events accommodate as many attendees as space allows. Some events do not require a ticket such as seminars, film, or anime events. However, to ensure you have a seat, it is recommended you acquire a ticket to these free events.