What happens when you fuse?
On a high level, the NFT and your pod get linked, and your pod gets transferred to the iNFT Smart Contract. You will retain ownership of your NFT in your wallet. Since Fusion is on-chain, you will incur gas fees. If you sell your NFT while it is fused, your pod will still be linked to the NFT and thus you will lose access to the pod. If you would like to sell only the NFT, you should unfuse it before you sell it.
On the smart contract level, we record: the NFT contract, the NFT ID, the Personality Pod Contract, and the Personality Pod ID, and we assign an "iNFT ID" to the newly fused iNFT. The smart contract has an immutable record of that particular NFT being fused with that particular Personality Pod - this information can be retrieved by any DApp that is built on top of the protocol - and that helps the DApp know which NFT is an iNFT and which NFT is just an NFT - and so fusion helps create a decentralized record of all the iNFTs in existence.