funny about this.. i've posted the same sort of thing 2 weeks ago on the propellerheads site for reason
even if you haven't got an amazing setup , you notice the difference in the eq.. depends on the sounds your using though.
I use a lot of harsh / heavy sounds, that fill up the frequencies, so they clash and when you eq cut certain ranges on certain sounds, you notice a big difference, same with side chaining, for me it's a must the kick drum is more prominant, so it's very punchy.
computer music mag, sometimes has a PDF file of frequencies, that show the area's where you can cut and the muddy area's say for vocals , piano etc.