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.  When a CPU runs out of work items, it borrows a free work item from another CPU.  An increasing value of this running counter might indicate the need to increase the 'MaxWorkItems' or 'MinFreeWorkItems' registry values for the Server service.  This value will always be 0 in the Blocking Queue instance.