Let’s you know the ticket is authentic because you can see it is part of the set of tickets the band/venue initially created, because of atomic transactions I can guarantee if I send you money I’ll get a ticket in return (NFTs are just another form of currency at the end of a day), because they’re unique I know no one else can own it even though it’s all public so I won’t have issues at the door, because they allow metadata the venue can confirm if they’re resellable or not on the NFT itself, a venue can get a % of resale value back allowing more second-hand markets to exist, among various other possibilities.