Stamping attendees is a great way to ensure no one gets into your venue who isn't supposed to be there. If your event requires a physical ticket, for example, stamping the ticket-holder when you give them their ticket ensures they can't swap with anyone else. Alternatively, if you run a nightclub, you may want to allow people to leave the venue to smoke then re-enter without joining the original queue; stamping party-goers as they enter shows you who can skip the queue.