filtering a drum loop

I don't understand this method of production. If you got your drum loop happenin, why would you run the whole loop through a filter? To grunge up the loop? What kind of filter? a comb filter? a combination of filters?

I can understand filtering individual drum hits. Is it a better production technique to make your loop first, then remove offending frequency's rather than removing offending frequency's from individual hits?

:?:

Its more of a creative effect.

often used in transitions and buildups, but it's pretty obvious what's happening.