On MacOS I use a custom password for keychain. so the only way to see the saved passwords is with this 'master' password you setup on Keychain.
It is useful if another one has to access to your mac and you have to tell than you user login password. As the login password is different than the keychain password, this person will not be able to access the password on keychain.
I would like to know if there is this same feature for IOS. Some times you have to share your iPhone password with someone you know. But you do not want they to go in preferences and type you iPhone default passwords and see all you saved passwords on safari.