Benefit: establishing the mechanism for permission-less transferring of assets between Ethereum and Bitcoin.
Cross-chain transfer between Ethereum and Bitcoin is useful in fields such as:
Stable coins: External chain assets such as BTC could diversify the collaterals used in stable currencies on Ethereum.
Decentralized exchange: Ability to transfer external assets onto Ethereum expands the available assets for trading.
Financial derivatives: Interconnecting blockchain based assets opens up possibilities for various financial derivative products.