By default, all Authy 2FA account tokens are stored locally. We don't keep a record of the accounts you add, so the loss or failure of a device could result in you permanently losing your 2FA account tokens, or access to your important accounts.
Enabling the backups function in Authy tells us to save an encrypted copy of every 2FA account token on your account. This allows you to easily recover 2FA tokens if needed, and synchronize them between multiple devices using the same account. We recommend all users enable backups, and configure a second Authy device as a sort of "insurance policy".
For more help, see the following resources:
Notice: Enabling Authy backups only saves an encrypted copy of your 2FA account tokens. Your backups password is never transmitted to Authy, so we are unable to recover a lost or forgotten Authy backups password. For more details, including information on recovering access to your 2FA accounts, see Authy Backups Password Recovery.