NCQ works well when many writers are trying to get access to the hard drive. Of course this works well, unless you attempt to do more IOPS than your drive array supports for a continued amount of time. At that point applications that require fsync or write barriers will get terrible performance due to latency , and you should re-evaluate your storage. Which is the whole point of queues don't fix overload.
Yes, having a queue can help in optimizing the throughput, but only if it exists some economy of scale by combining some tasks (which is the case with NCQ). But the when the queued tasks are completely independent, then having a queue doesn't help in increasing throughput.
