"To simulate graphics environments without incurring the overhead of user-space graphics drivers, we have implemented the NVIDIA Persistence Daemon" Most users wouldn't want this, so it makes sense it defaults off
AFAIK, from what i had read in past: The real effect of that service was to make the driver save the Graphics memory to disk and restore upon resume...
But to be sure it solves other ppl's problems with sleep/resume on nVidia you could ask them to try that command and ask for feedback. Just so you don't enable it for nothing in anycase...