As I've understood it, there is a limited amount of room in recorded audio; the article has it stated as between 20 and 20 000 hertz. If two different instruments occupy too much of the same frequency, they start overlapping and you get a "muddy" sound. So in order for every channel (instrument) to be heard clearly, you cut away the non-essential parts of the sound with the equalizer-settings, thereby making room for other instruments.
Though something tells me I should focus more on playing and composing first.
It's pretty strange, of all the orders I've made from abroad (which amounts to pretty many now, I think) only one has been picked up by the customs for inspection. Let's hope that keeps up.