This is the hypothetic use case I came up to learn about smart contract programming.
I am trying to create a ERC721 Smart Contract that would mint tokens for photographers who want to sell their work. The photographer uploads a picture and I put it somewhere and include that link as the tokenURI for my UniquePhotoNFT.
When I mint a new token of UniquePhotoNFT, it has an ID (1,2,3,4, etc) with all different token URIs. All those tokens belong to me as I am holding all those tokens for my users (so they don't need to deal with any of the blockchain staff).
When someone comes to buy a UniquePhotoNFT with token id 3, I can easily transfer that token 3 to the buyer's address. However, if the new owner decides to sell the same token to someone else, how can I make the transfer on their behalf? It won't let me do it because as the contract owner, I am not the token owner.