In that case, command queuing is a winner all around, right? Not necessarily, because command queuing introduces a slight overhead to the drive's access times. In a typical server environment, queue depths are high and requests are random, so the performance gained from command queuing more than outweighs the overhead. In a desktop environment, a drive is rarely asked to service more than one request at a time, so when NCQ is enabled most of the time the drive is "reordering" a single request. Even in heavy drive access multi-tasking scenarios, queue depths don't generally exceed a couple of requests.

The occasional performance improvement when there is a queue depth of greater than four requests does very little to claw back the overhead of NCQ or TCQ. Desktop applications typically suffer around a five to ten percent drive performance deficit when command queuing is enabled. Would you notice this performance drop? Maybe not, but it's along the same lines as slightly overclocking a CPU or graphics card. Turning it off is technically faster, so you may as well.