You can search virtually every field in one master search. Your site visitors can set e-mail reminders on any event in your calendar. You can provide a Value-Added Service to your site visitors. Add similar events without having to enter all the information every time. This will save you TONS of time when adding recurring events.
Events drop off automatically when the event passes.
Your site will never have old events on your calendar. You can allow the public submit their own events. You can let others submit their own events to your calendar. You don't have to remember the exact spelling when searching. You can sort anyway you choose.