So i still dont understand one thing...guitarists who have expensive and great valve heads and cabinets have distortion pedals in theyr pedal board
for example Cannibal Corpse guys have Mesa Boogie Dual and Triple Rectifiers but they still have Boss MT-2 in theyr pedal boards...and Daron Malakian uses the same Boss pedal and he even says "its the best metal distortion"
Maybe thats why canibal corpse doesnt sound that amazing... HOWEVER! Each person has their own personal preferences. Most people simply use an overdrive just to tighten up their amp's gain. Boss MT-2s are horrible by the way...
I wonder the same thing.

But some people like different levels of gain. alot of people use different tones for different songs. But I don't think CC really cares about tone.
It's possibly just for different tones or just a boost, or also to tighten up the sound. And CC have incredible tone!