ok. i have been hearing about IB sub setups...wtf is this? is this better than a regular sub??? i have been told that it is...why would someone do this??? and if it is better, why doesn't EVERYONE do this??? please help me understand??? thanks

Axiom M60Ti Infinity 2000.6 x 4 Infinity RS1 rear Infinity CC200 HSU VTF3 - MKII