Once the date of the event has passed, the event will automatically become expired. Expired events are denoted with a red expired tag next to the event in the list.
Expired events, although they are visible in the dashboard, are not displayed on the website. This is very useful as it reduces your website management and you don't need to remember to take down event or delete it after it's over. It just happens for you.
If you have a number of expired events in the event calendar you can just click the "Filter by Date" drop-down in the search and just select "Upcoming" and only the recent and upcoming events will be displayed for you.
You can delete expired events if you like, but this is not required. If you have an event that will be returning, you can just change the date and all the old information will still be there. This is another time-saver for website managers, so you don't have input all that info again.