This feature, that works in the desktop version, is immensely useful for both users and mail service providers. Our customers has an autoconfig.theirdomain.com DNS records, that means easy setup in Thunderbird, as it knows our servers and settings.
Not all people will have Thunderbird installed, and can use the QR scan - Some people will want to use a webmail and on the go, they want a (good) mail app, like Thunderbird. So the same concept of Autoconfiguration should work here.