Command queue controlling


hallo there,
i’m kind of confused about these Command queue controlling statements ,even if i read the api-document, something like dType.SetQueuedCmdStartExec(api) and dType.SetQueuedCmdStopExec(api). Can any one tell me where should be these statements used and what happend without these statments. i will appreiciate if you can explain it with a example

thany you very much