Noise cancel does not adjust the sensitivity of the detector or compensate for soil minerals. What noise cancel does is divide the frequency of operation into 11 groups of 28 frequencies. One of those 28 groups is selected based on the frequency of external electromagnetic energy that can induce a signal into the coil from sources such as a transformer. Each group of 28 is called a channel so the quietest channel, group, is selected.
Noise cancel should be done anytime external noise is suspected. An excessive static like sound in the threshold is one way to tell we need to noise cancel. This can be seen on the digital screen by flickering of the digital reading and when using the crosshairs they jump around in a flickering manner as the digital reading flicker.
I cannot imagine how the idea got started that we should not noise cancel or that experienced users don
