Run promotion campaigns prior to the festival to increase awareness and ticket sales.
Provide all necessary information during the even like where to find the toilets, food, drinks, stage 3 etc.
You can ask for playing bands and get more information, links about them and their playtimes and locations.
Furthermore it can be used as an (emergency) notification system for time sensitive announcements.
After the event you can gather feedback and even sell tickets in advanced at a special rate for the next event.