physical security keys

Hello im_scott,

Thanks for reaching out to Apple Support Communities. We see you have some questions about Security Keys, and we'd like to help. We also see you came from a great article about this, as well. About Security Keys for Apple ID - Apple Support

The following information can be found on that article, and explains why they are used with many:

Security Keys for Apple ID is an optional advanced security feature designed for people who want extra protection from targeted attacks, such as phishing or social engineering scams. 

The article can also help explain how it works for both your iPhone and MacBook.

Please let us know if you have any questions.

Regards.