Metadata isn’t part of the core spec, so NFTs don’t have to link to anything. You can only verify ownership of the NFT id. What is represents is up to the author. It could be a credential to a web application. It could be a pass to a venue, checked at the door, it could anything to gate access by asserting if the wallet holder, account, etc has a specific id or balance greater than zero of said NFT. An NFT is a unique token. What builders do with it is up to them. Mostly it’s been art. What else could builders do when they have a permissionless way to assert that a user owns a unique digital id (NFT). It’s worth exploring more.