So you can have infinite and separated set of addresses at your own disposal based on the passphrase while having one single private key in the form of the seed? That's neat. Thank you.
That's not quite right. There's one
mnemonic, that's the 24 word string. Combined with
any (or no) passphrase, the mnemonic gets turned into the seed, and then the root private key. Each passphrase you use with the same mnemonic will generate a different root private key.