The paper key process after the initial login is broken.
Because I didn't have an actual piece of paper with me when I tried the app (and writing down things like that on paper is a weird idea anyway) I opened 1Password to create a secure note there. Unfortunately, when I returned to Keybase the app had already silently moved on to the next screen without me having confirmed anything.
I'm not sure what this paper key will be needed for in the future but I hope it's nothing important.
If you lose the device key on your computer (perhaps there is a hardware error or it is stolen), you can use the paper key to add a new device key to your account - and not lose any data.
You can add another paper key using `keybase paperkey`, and you may want to revoke the old one using `keybase device remove <key name>`. This is also possible to do from the "Devices" tab in the desktop or mobile app.
Of course, if you have Keybase both on your computer and your phone you already have some redundancy, and maybe having a paper key is not as important.
If for some reason in the future you lose access to the devices you have already logged into Keybase with then you'll permanently lose access to that account with absolutely no way to recover any of the files, messages, etc... it contains. It may be unlikely you'd lose access to multiple devices at once but seems risky to even continue using that account without the paper key. Luckily you can generate a new one from the app.
Because I didn't have an actual piece of paper with me when I tried the app (and writing down things like that on paper is a weird idea anyway) I opened 1Password to create a secure note there. Unfortunately, when I returned to Keybase the app had already silently moved on to the next screen without me having confirmed anything.
I'm not sure what this paper key will be needed for in the future but I hope it's nothing important.