Do you adjust your subwoofer

Often.     My subs came with a remote that controls all the subs Optimization parameters and its six customizable presets.. 

Slight volume adjustment are used mostly. Possibly one or two presets which embellish some aspects of the recordings low frequency to my taste which lie below the established crossover region (100Hz - 33Hz).

I'd like to second @mijostyn clarity regarding -6dB sub-bass products. Don't you just love it when someone does the math? Nice.           

"@akgwhiz Glad to see that not everyone buys into set and forget it" Me too! It's literally the most fun we have with our system. My preset for Rap KILL'S it.

My 2 RELs crossovers are adjusted at the point where the main speakers drop off, with the sub levels and phase checked once in a while. I have a Schiit Loki Max EQ and use that in there a little bit if a recording needs it. 

I’ve two REL Carbon Special and occasionally I’ll bump the volume up a notch when I pull the screen down and watch a concert DVD. It’s a bit of a nuisance with the RELs as the gain knob isn’t marked with positions and I can’t feel the notches which are supposedly there. Also, a couple degrees of adjustment results in too much or too little volume. Fantastic sounding subs but ergonomics could be so much better. LEDs on the sub with remote volume would be bliss!

I would also like to suggest that every audiophile should have a calibrated measurement microphone and program. You will never know what your system is doing unless you measure it. A good program will also give you group delays which will allow you to integrate the subwoofer better.

It is also important to note that the low pass filter supplied with most subs will never integrate a subwoofer to maximal effect. This requires a complete 2 way crossover preferably digital with room control and delay capability (digital bass management)

Removing the low bass from the main speakers increases head room and lowers distortion. It is like doubling the power of your amplifier. 

A proper sub system is a set it and forget it item. I use my system for theater also and I never change settings for theater. The proper adjustment is proper for everything. 

I get that a calibrated to room setup is ideal.  Its the goal. An "all else being equal" thing.  But it requires a test tone/sweep.  Then an actual recording comes up and guess what, you may not feel that they mixed the bass high enough or maybe way to high.  I don't feel it's wrong to adjust it.  Do we sometimes add salt or a sauce to a cook's preparation even at a good restaurant?  I use a hi-pass on my mains, appropriate sub cut-off etc but there are some recordings that just don't seem to have enough bass at all.  Less common,  some seem too hot.  My 2 cents.