Off-line backup is basically designed for notebook users who are off-line most of the time and cannot rely on the backup schedule to backup regularly.
The "Backup Interval" allows notebook users to specify the interval that they would like their data to backup. When the machine is online and this interval has elapsed, backup will run automatically. If [Off-Line Backup Alert] is enabled, a popup message box will ask the user to confirm starting the backup.
The [Email Notification] setting is the number of days since the last backup that triggers the backup server to send email notification to the client to remind him to run an off-line backup. When the [System Logout Backup Reminder] setting is enabled, a popup message box will ask the user to start a backup before logging out / shutting down Windows.