My experience is that cab insulation works best with ported cabs.
My Krank 4x12 sounded really dark and overly tight. Artificial sounding really.
I then found that the cab was ported, which I didn't know. Anyways, I removed the batting that was stapled to the back and sides. I left the batting on the top and bottom though. The cab sounds better. Big difference in response as well as the bass and treble. More snap and livelier at high volumes.
I put the batting from the Krank on the back of a sealed Marshall 425A and couldn't hear a difference at all. So I guess that's why you see it lots in ported guitar cabs and ported bass cabs. Some home audio/theater stuff too.