The Command line tool can help in situations when the built-in scheduler in the Web UI doesn’t suffice. Think of running the backups using usnig multiple identities, scheduling backup tasks after reboot, logon, lock screen or an event. You can use the Windows Task Scheduler to do this, but this is not (yet) implemented in the built-in scheduler.
I suppose at least every time the Web UI is started, optionally with added scans at regular intervals. To speed things up, the Web UI engine could check timestamps of the local databases used by backup tasks. If a timestamp has been changed since the last check, a query could be executed to check for updates.