If the Halt backup immediately option is selected, any error encountered during the backup process (such as the failure of one feature) will cause the entire backup to halt. On the other hand, the Continue option will not halt the backup just because of a single failure. For automated backups this is superiour, as a partial backup is better than none at all.
When set to Continue and purging of old backups is enabled, the purge
will still be done even if the backup fails.