User blog comment:UsoppThePotato/Let Corki shine again!/@comment-8506165-20140216172139/@comment-7118467-20140216211409

In the end this build puts Corki more into a supportish role. Though he will still deal significant damage, the focus lies on the armor shred. With you E and a black cleaver you get 40 flat + 25% armor penetration, which can be really significant in the current meta. The problem with ADC Corki is that you cannot use its full potential simply because as an ADC he is squishy.

So basically the purpose of his build is shredding armor so your ADC/Marksman(i prefer the latter) has an easy time killing the enemy tank, and even though tanks should not be the focus, what is a team supposed to do in teamfights when the tank just melted away?