This mode will use a remote node whilst also syncing the blockchain. This is different from the first menu option (Simple mode), since it will only use the remote node until the blockchain is fully synced locally. It is a reasonable tradeoff for most people who care about privacy but also want the convenience of an automatic fallback option.
Temporary use of remote nodes is useful in order to use Monero immediately (hence the name bootstrap), however be aware that when using remote nodes (including with the bootstrap setting), nodes could track your IP address, track your "restore height" and associated block request data, and send you inaccurate information to learn more about transactions you make.
