T-man nailed it. A peak that huge in the lower bass range will lead you to set the bass according to that level, which will make all of the other bass sounds seem lifeless or nonexistent. By removing that peak with the EQ, placement, and/or room treatments, it allows you to actually the raise the overall subwoofer level without that one extremely loud peak dictating what you hear (if you have that one note that shakes your room, you're going to set the level so that one note doesn't pound your skull into submission; but, in doing so you make everything else too low). With a flatter in-room frequency response, the bass sounds fuller and more balanced.

Absorption is more beneficial in the higher frequencies. With the bass range, it's more about the placement, room dimensions, and equalization. Bass traps in the corner are more effective than other room treatments.