Flow sampling reduces the CPU overhead of analyzing traffic with Flexible NetFlow by reducing the number of packets that are analyzed. Flow samplers are used to reduce the load on the device that is running by limiting the number of packets that are selected for analysis. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/fnetflow/configuration/15-mt/fnf-15-mt- book/use-fnflow-redce-cpu.pdf