[Koha] zebraqueue and cron jobs

Appendix 12.2 to the new Koha 3.2 manual suggests running rebuild_zebra.pl as a Cron job every n minutes. However, the zebraqueue_daemon appears to automatically update the biblio database as and when needed. Could someone kindly explain the necessity of the Cron job? We are having a few problems finding sufficient "system level" documentation. Many thanks - Paul --- Archives and Collections (ACS) Society 205, Main Street, Picton, Ontario, K0K 2T0, Canada Canadian Charitable Organization 88721 9921 RR0001