http://www.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/deeplinks/2017/09/guide-common-types-two-factor-authentication-web
Also, if you log in frequently on different computers, it can be inconvenient to unlock your phone, open an app, and type in the code each time.
Push-based 2FA Some systems, like Duo Push and Apple's Trusted Devices method, can send a prompt to one of your devices during login. This prompt will indicate that someone (possibly you) is trying to log in, and an estimated location for the login attempt.