I’ve seen some good videos on denoising but bear in mind that it’s changing again in dartkable 3 and I haven’t seen any videos covering profiled denoise on this version.
This thread (Changes in noise reduction for darktable 2.7/3.0) has some useful info on the new settings but the long-and-short is that the two-instance approach is no longer recommended with the new version of the profiled denoise module.