Setting within the syncthing config which when enabled, will allow you to have multiple users and requiring the users to login to access the web ui and manage folders and devices.
Use Case
This will be useful for running a syncthing provider were other can sign up and use your service. This way you can have one installation of syncthing on one server instead of having a server for each user.
Admin & Regular Users
The admin user will be able to shutdown, startup, restart syncthing, decide how much storage each users has, pause syncthing for any users (Useful for payment systems if users has jot renew their subscription) and others tasks only for the owner of the server to have access to. A regular user is restricted and can only do basic tasks. Each user will be able to manage their own folders and devices.
Subscription
And to have a value in the database for every user to determine when their service will end such as a date and when the date passes, syncthing will be paused for that user. This will be useful for syncthing providers to offer syncthing as a service to backup and sync files for users.
Login/Signup
User/Accounts should require an email, password and for additional security offer TOTP 2FA.
Create/Delete Folders
To allow the users within the syncthing web ui to create folders and delete folders
Conclusion
All of these features are optional and can be disabled and should be disabled by default and are not needed for the regular users running a syncthing client. These feature are used for syncthing running on a server. The syncthing web UI is great and with these features, one can signup to a syncthing provider such as syncnow.com and can login into app.syncnow.com to access the syncthing web gui as a users.