I think it is smart to actually get quieter as the mix session goes on.  Often it is the other way around and it can creep up in volume instead.  But I feel at lower volumes you are often more in control of the mix.  I still like the mono Auratone type speaker way down at very low volumes a lot.  This is really good for the sticky outs things.  Anything that is even slightly too high is accentuated on the small mono speaker.  It leaps out on that. 

Great info guys!!!  Thanks Jeff.

Hello, I did not read the article, but did read the thread.  The bulk of my mixing and what not, are performed at 70-80 db.  I find that level to be quite comfortable.  I do follow Jeff's advice that sometimes you need to pump it up to 95 db to hear the sticky outy things, but that is never for to long.
 
For me, and I don't really have any data, just anecdotal deduction, I follow this.  Because we live in a "loud" world, noise everywhere,( unless you live in a rural setting,) I need to factor in the amount of loudness I've encountered throughout my daily activities, lawn mowers power tools, autos, loud shopping environments, busy streets and restaurants... These all have a cumulative affect on my hearing organs.  In an effort to preserve those precious little parts, I wear earplugs a lot when I am out in the world. 
 
We know that our ability to hear certain frequencies is impacted by many things, and to me the sounds in my "hermetically sealed studio" are not what I worry the most about.  It is the cumulative affect of noise throughout the day that contributes the most to my ear fatigue. 
 
But, as I said 70-80 db for me, with dedicated spl meter at my fingertips, seems to be the sweet spot in my room.
 
JQS

I change the volume all the time when I'm mixing. I feel it helps give you a broad oversight of your mix, and is important because at the end of the day, people are going to be listening to your mix at all volumes! As Jeff says, if something is sticking out too much that will be far more obvious at low volumes, but it's also easier to hear what compression settings are doing at low volumes. I find this especially with mix bus compression - if you've gotten the settings wrong or are applying too much, this becomes especially apparent when you listen to it quietly. 
 
I also find it important to check on headphones now and then too. If you have a good pair of headphones that go down to 20Hz and you've flattened them with something like Sonarworks, they help in checking the bass, especially if your room isn't perfect. And since a huge proportion of people ONLY listen to music on headphones these days (especially kids), making sure your mix sounds good through them is very important. Personally I'm not a huge fan of how music sounds on headphones and I have a very low threshold past which I think "ew that sounds horrible" through them. A really well done pro mix, however, sounds great through both speakers and headphones. Things can end up sounding claustrophobic and cluttered through cans if you're not careful, and many a time I've gotten things sounding very open and airy through the speakers only to find that they didn't sound that way through headphones at all, especially if the low mids are too much.  

i love the sound of headphones, and the more extreme the mix, the more i like it!
 
maybe it's because i can hear multiple things at once, and clearly define them inside the mix, and i like the idea of picking it apart, i just have a good ear.
 
that said, 
a mix that comes together so seamlessly, where you don't notice any mix elements at all,
is magic to me.
i rarely mix that way myself.
 
 
i find that checking mixes with ear buds that have extended bass,
will clue me into low end issues faster than any other source.