How to replicate Lightroom calibration tool in Darktable

[EspE1]

Good information on channel mixer also here:

Please help me to understand "Channel Mixer"

I am very confused what is the purpose to adjust other colors in certain color channel. I understand basically there is a color wheel, what color is opposite of what color, however the other colors (e.g green/blue in red channel) don’t seem to follow the rule at all. The Rawpedia has some very limited information, I am looking for some better tutorial, and ideally some real world examples - how to achieve some effect by adjusting what. Thanks