There's a debate on how much denz you should use. For instance if you have a 1000 iterations render i set my denz to 999 or 990. Some guys like to set it to 100 less than the iterations or 50 less etc..
IT does speed up one's render times an make the render look better but i've found it acts a lot like Photoshops Reduce Noise filter. If your rig is pretty high end then using denz is not really necessary...
Like I said, haven't upgraded Daz yet so I don't know what I'm talking about entirely.
But still, iteration count depends on the scene, doesn't it? More detailed object, characters and world usually take more render iterations to get a good look than a scene with just characters. At least that's what I've experienced. Usually without a proper background in the scene, it takes about 300-400 iterations for my render to look good enough for me. So setting the denoiser to too high a value might just keep it from ever running.
Although I have practiced rendering in 1.5-2x resolution dimensions and downscaling it in photoshop later (just so I wouldn't have to wait for the rendering to reach a certain un-noisy state). Downscaling larger renders also removes much of the noise and sometimes even makes the image sharper without any loss of quality.
So what I'm saying is, I'm thoroughly excited to try out this new tool and see how much faster and/or better my renders will be.