You can also designate an email address which, in an emergency, can be sent a link to disable the feature. WhatsApp highly recommends this as a fallback, just in case you forget the code. It's a different approach to most technology services, which typically send a randomized string to your phone over SMS. To help you remember, WhatsApp says it will ask for your code "periodically." An inconvenience, sure, but a trade-off we would argue is worthwhile for greater security. If the app is your primary mode of communications, you owe it to yourself to turn this feature on.