So, we found out that a normal or passive agent waits for the server to connect, while an active agent connects to the server, grabs a list of items to check, and then reconnects to the server periodically to send in the data. This means that using one or the other kind of Zabbix agent item can impact performance. In general, active agents reduce the load on the Zabbix server because the server doesn't have to keep a list of what and when to check. Instead, the agent picks up that task and reports back to the server. But you should evaluate each case separately: if you only have a few items per host that you monitor very rarely (the update interval is set to a large value), converting all agents into active ones that retrieve the item list more often than the items were previously checked won't improve Zabbix server performance.