The motivating case was when you're in physical proximity to the destination device, but don't have any account linkage between the two (not even messaging/email/social accounts that are connected). The original idea came from university computer labs: transferring homework between the lab computer and a personal one was a pain. I had to sign into dropbox in the browser (and 2FA), or attach it to an email, or carry around a flash drive (which wouldn't work on phones), or whatnot. Just to move the file three feet. A glanceable code with no sign-in bridged that gap.
Other use-cases include people you don't know very well (and therefore don't have an email, phone number, etc.). We demonstrated the prototype to a crowd by uploading a file with the code visible on the projector, and suddenly everyone in the crowd had the file. That was pretty cool.