Today at a thrift store I found a JBL subwoofer. As soon as I got it home I hooked it up to my system and tried patches with a lot of low-frequency energy. What can I say? Bring on the Gran Casa. Now I know why I never used the bass drum effectively; I couldn't hear it. Lows in double bass are incredible, timpani hits and rolls are gut-shaking. Listening to mixes of mine, I realized there were holes where bass wasn't handled consistently through a piece because I had no way of hearing the frequencies.
Now that I have the capability, I have to make sure my mixes sound good with and without the subwoofer.