It's like taking a selfie, with the ability to keep both hands in frame.
Candid camera
I'm sure your photographer is excellent and will do a great job getting those group shots. But what about people just goofing around? Let the photo booth take care of that for you.
Ice breaker
With the privacy of a phone booth and the publicity of the internet rolled into one, a photo booth allows even the shyest person the ability to come out of their shells.