I've read several things (admittedly mostly on forums) where you should only use a sub to check your mix occasionally. Well, happy birthday to me, I got one (KRK 10s) and got it set up tonight.  I set it up using this article from SOS: 
 
http://www.soundonsound.c...rticles/subwoofers.asp
 
I think, if I read the article right that the goal is to have the sub on most of the time. I still plan on checking my mixes with the sub off and I also have one of those Behritone Auratone clones for mono and small speaker checking.
 
Does anyone here use a sub most/all the time?

I use my sub pretty much all the time. As long as you have it dialed in correctly, it's indispensable for letting you know what's going on with your low end. It's equally important to hear how your mixes sound on bass deficient systems though. But once you learn your monitoring environment with the sub, and how it translates on real world systems, you'll probably find that you have your sub on most of the time too.

Thanks Leadfoot. I've been listening to varied musical genres since I got it going to get used to how things sound with it and I'm really liking how everything sounds. 
 
It's kinda funny, I first set up the sub from the KRK manual and their website where you download test tones and use an SPL meter to set levels. After dong this, the sub was WAYYYYY too loud.  I then followed the SOS article (above) subjective way to dial it in and that worked much, much better.

Yep..I let mine run all the time. The only time I turn it off.... I have it plugged into a switched power strip for that purpose.... is when I need to double check something in the low end.

If it's set up properly, you should be able to let it run.  If it's not set up properly, and that tends to be most often,  "the sub is a bit too loud" the mixes will show it by being mixed "bass lite" .  Very few people add a sub and don't turn it up loud enough because that's the problem they were trying to solve by buying one.
 
Getting the proper balance is very important. Once you get it set.... trust it and don't touch the level control or the crossover freq knob.  If the bass is then too loud or too soft, fix the mix, not the gear.
 
It's ear candy for the bass and kick.  I love what mine did for the sound I hear.

All the time. After my first couple of mixes with it, I had the sub level set to where I can barely hear it most of the time, but it's there. If I start to really hear it, I know I've gone too far with the bass/kick in the mix, unless that's what I want.
 
Regards,
Dan

This is weird but it works for me.  I love my subwoofer, but I'm honestly getting better results checking the bass on headphones and spending more time mixing and listening on this thing and more time listening in mono.  I run a line to it from my headphone amp and put it directly in front of/below my computer monitor and lean it back to it points right at me.  I can get a mix I'm happy with using just this and headphones actually.  After that my Mixcubes in mono first, then stereo, then my regular monitors, mono first, then stereo.  If someone had told me this six months ago I would have called BS, but I'm happier doing this this way.  If I can make it comparable to a commercial mix on this and bass is good on headphones, it good.  If it was desert island mixing, I'd probably go with just this.
 
http://www.amazon.com/DKnight-Ultra-Portable-Bluetooth-Microphone-Blackberry/dp/B00F5NE2KG/ref=sr_1_1?s=electronics&ie=UTF8&qid=1443616857&sr=1-1&keywords=bluetooth+speaker
 

Same here. The sub's on all the time. I rely on alternate speakers and headphones to hear what it sounds like without that low end help.
 
But it took me awhile to get the sub placed and adjusted right. There is a natural tendency to turn it up too loud. I'd recommend recording a stepped or swept sine wave series to check levels and, more important, to identify your worst low-frequency room modes. The sub is going to excite problem frequencies that might not have been noticeable before.
 
Another tip: where you put the sub relative to the mix position is very important. As you're experimenting with different locations, keep in mind that it doesn't have to be directly on the floor and it doesn't have to be midway between your main speakers.
 
Depending on the type of floor (e.g. hollow space beneath vs. solid concrete) it can benefit you to raise the speaker off the floor and/or add some vibration dampeners underneath it.
 
Moving it off-center can help by changing the resonant peaks such that they're not reinforcing harmonics from your mains. For example, I have a 70 Hz resonance in my room, which means it's also problematic for multiples of 70 Hz (140, 210, 280 Hz, etc.), which my mains contribute to. Moving the sub to one side I found a spot where 70 Hz is not peaking at the mix position, so even though the mains are still resonating at least they're not conspiring with the sub to make it worse.
 
Set your crossover as low as possible. Figure out where your mains start to wimp out and set the crossover just above that and no higher. You might think that setting the crossover higher will help by taking some load off the mains, but in practice it's not going to be as smooth that way. My main speakers' -3dB point is about 50 Hz, so my crossover is set to about 55 Hz. Originally I had it up around 70 Hz but heard an immediate improvement after lowering it.
 
As with any new speakers, listening to commercial music and training your ears is the best preparation. It's a tough assignment: kick back and listen to your favorite tunes through your new setup, for as long as possible. After a hundred hours or so, all the technical stuff won't matter because your brain will just know what it's supposed to sound like.

Sub on!  I'm able to quickly check without the sub with a button press on the monitor matrix.  Check with multiple speakers sets and headphones ... even with 8" monitors there is a lot of improvement.
 
Getting it tamed/dialed in took a LOT of time and tweaking though

i never use a sub.
 

Thanks for all the responses guys! It really makes listening to my music library that much more enjoyable. Right now, when I turn off the sub I can tell there's something missing but turning it back on it's not quite so noticeable. I hope that means I've got it set about right.