I think idea is that you don't backup secret key material. You should add multiple keys to your logins and have a "backup" key which is separate one. Especial

I think idea is that you don't backup secret key material. You should add multiple keys to your logins and have a "backup" key which is separate one. Especially when you lose physical key, you want to have different one and revoke lost one asap. The same with private keys generated on a device - private key should stay on the device on which it was generated and never copied. If you need access from a different device you generate private key on another device and transfer public key only to be added to account. Which in turn also makes physical keys that you can connect to different devices a bit more convenient as private key never leaves key and is not directly accessible by laptop that it is connected to.