Apple ID is important to access your iPhone or other Apple devices like Mac or Apple Watch. It helps in maintaining your applications and associating the data with your iPhone.
It connects your device with iCloud and transfers all the data stored on the phone directly to the iCloud. Apple has an additional security feature called the two-factor authentication to secure your account.
This requires users to verify identity using any of your Apple devices. Users even need this before they make any purchases on the App Store or iTunes or sign in to a new device.
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