If you set an encryption passphrase, this passphrase is only used to encrypt the / partition while all other partitions are encrypted via keyfile, which is stored somewhere under /etc. This way you don't have to enter your passphrase multiple times for each partition beeing unlocked.
But if / is chosen to not be encrypted, archinstall still uses keyfiles to encrypt the other partitions, and doesn't use the passphrase at all, which is not was most users would want.
If you set an encryption passphrase, this passphrase is only used to encrypt the / partition while all other partitions are encrypted via keyfile, which is stored somewhere under /etc. This way you don't have to enter your passphrase multiple times for each partition beeing unlocked.
But if / is chosen to not be encrypted, archinstall still uses keyfiles to encrypt the other partitions, and doesn't use the passphrase at all, which is not was most users would want.