The article is informative. That means, passphrase can futher protect your cryptocurrencies. Like the Trezor used as an example, if it is stolen, but you have already set up the passphrase, the theif will be unable to access your wallet unless he knows the phrase. Wallet owner is the only one that can reveal the passphrase.
Passphrase can help as additional protection, but it is susceptible to brute force if not complex enough. In the case of Trezor or any other hardware wallet based on Trezor (all clones) someone has calculated that at least 37 characters are required for the protection to be adequate. Such an attack is currently not possible on Ledger HW, and one of the most important differences between Ledger and Trezor is in
The Secure Element which is special chip built in Ledger hardware wallets.