Just for kicks, I was listening to Bavarian polka music -- you know, oom-pah music -- and I decided to turn off the sub to compare the sound. The notes stayed the same, even for the oom-pahs, but the punch (both from the tuba and the kickdrum on the beat) was gone. And that's with a 100Hz cross-over. I suppose the occasional oom (n.b. the pah is usually higher in pitch) might have been down a few dB, but definitely it was the "feel" that was most missing. I have M3Ti mains and TN-1220HO sub.
--Martin