12 Words + Passphrase == 12 other words?

[Chikito]

Save it also the private key if you want to be more secure and paranoid if the resulting address is different after adding Passphrase.

Because there are have possibility of negligence if someone uses an additional Passphrase, like forget an uppercase letter, symbols, numbers, etc.

Passphrase is sensitive, just a little bit wrong put . (dot) You will got the different address generated.

wallets cannot identify like we use passwords. the wallet will remain open like there's no mistake when put wrong passphrase

[Saint-loup]

To be honest I don't understand the point of storing a the private key (the master private key actually I guess). Why not just using a seed without passphrase in this case. It would be more easily usable at least. It produces another weak point in addition, because someone finding your master private key will be able to steal your funds without needing your seed and your passphrase, so your funds can be stolen by 2 ways (with the master private key and with the seed and the passphrase) instead of only one.