This indicates the storage type of this policy's conceptual row, where a value of nonVolatile means the configuration will be preserved across a reload. Getting this wrong is a specific, common operational trap: a carefully tuned resource policy left at the default volatile storage type will silently vanish the next time the device reloads, with no error to warn the admin. An admin who configures a custom ERM policy but forgets to set this to nonVolatile would find that policy completely gone after the next maintenance-window reboot, with thresholds reverting to whatever, if anything, is baked into the startup config.