Lots of systems have multiple interfaces for monitoring, particularly enterprise hardware. As one example, we have the Agent installed on a HP server. The HP server also has an iLO interface, we would like to add OID's to monitor the array, disk smart status, temps etc.

Currently we have to duplicate servers, once with Agent install and again as a SNMP device to monitor hardware. This is not ideal as the device list gets messy.

In Zabbix you can add multiple monitoring methods to a single device (eg; Agent, SNMP, IPMI, etc etc).