Comprehensive and Detailed Explanation From Exact Extract:

Custom pollers are typically created when you need to monitor metrics or OIDs that are not supported by default in SolarWinds:

Monitor specific metric that is not out-of-the-box: If a device exposes a metric not natively monitored by SolarWinds, you must create a custom poller for that metric.

Monitor unsupported object ID: For any OID that is not included in default templates, a custom poller is necessary.

Monitoring special equipment or devices without WMI might also need custom pollers, but the requirement specifically applies when you need to access non-standard metrics or OIDs.