Every request from a client is represented in the server as a 'work item,' and the server maintains a pool of available work ...

Every request from a client is represented in the server as a 'work item,' and the server maintains a pool of available work items per CPU to speed processing.  A sustained value greater than zero indicates the need to increase the 'MaxWorkItems' registry value for the Server service.  This value will always be 0 in the Blocking Queue and SMB2 Queue instances.