blockchain.info hosts encrypted wallets, and all decryption is done locally, so having a Google Authenticator bound to a wallet only prevents an attacker from downloading that encrypted wallet.
Now, assuming the passphrase is good, having an encrypted wallet is perfectly useless if you do not know the passphrase.
So the two-factor authentication would provide any benefit only to people with non-good passphrases... but that wouldn't be a real solution: they ought to change passphrase anyway!
Hence, I can't come up with any situation were enabling two-factor authentication on blockchain.info provides any meaningful benefit.
Am I missing something?