The QoS stats tab lists QoS-specific information in the network. QoS or Quality of service is the most important factor that determines how effectively the available enterprise bandwidth is being used in the WAN. It is also an index of the overall User Experience of the available Bandwidth.
Here you see the top DSCP that is utilizing the maximum traffic from accross all the devices that are sending flows to the NetFlow Analyzer server. Also you can see the Device and Interface specific QOS information by clicking on the device or interface name on the right hand side view.