One common question we often hear on IRC is: how to make hosts depend on their proxy. The problem being that when a proxy is unable to send data to the server for a long enough time, the nodata() triggers on hosts monitored by the proxy start to fire.
A possible end result is illustrated perfectly by quoting one of the users in #zabbix @ irc.freenode.net
<someuser> lets say one of my large proxies falls behind. I can receive like 2k mails.
Obviously, receiving such a quantity of notifications doesn’t help you correct the issue.