The master key is a special passcode reserved for certain sensitive account actions that won't need to be performed very often. For best security, we highly recommend that you create a master key. But it should be kept very secure and separate from all your other passcodes. Creating the master key does the following:
Increases the security of account password reset (the master key must be provided for reset).
Allows you to obtain a two-factor bypass code for account login (the master key must be provided to get a temporary OTP bypass code).
Allows you to bypass the global settings lock so that settings can be changed immediately.