Google Advanced Protection Aims To Safeguard Those Most At Risk From Targeted Attacks
That Security Key is needed when you sign in on a new computer, browser, mobile device or if you get signed out. That is important because if you are using it on a single computer you won't be forced to use more complex authentication methods constantly.
Advanced Protection will limit access from third-party apps to your most important data, such as emails and Drive files to prevent exploits. This means that third-party apps will no longer be able to access Gmail or Drive; you will have to use the Gmail app or Inbox by Gmail for secure access. Access to Gmail or Photos will only be possible using Chrome browser.
If you frequently use Apple Mail, Contacts, and Calendar apps, they don't support Security Keys and won't be able to access your data. You will have to use Gmail, Inbox, or Google calendar apps on iOS for access.
Advanced Protection adds additional steps to unlock accounts when needed to prevent unauthorized users from gaining access. If you lose access to your account and both Security Keys, additional verification will take "a few days" according to Google to restore access to your account. Google doesn't give you the security keys; you do have to buy them and you can register for the program here.Google recently added barebones antivirus software to Chrome to help prevent infections and improve security.