Monitoring at low volume is good in order to lower ear fatigue and to protect your ears, therefore yes it is the winner in practice. But mixing at low volume is not the answer to a great sounding mix, definitely not. More than anything you need to mix such that the mix is interesting on many different playback levels and stays pleasant when cranked. But when cranked the mix is in its highest information density hence you get the most information about what the mix contains. Then you might notice you have issues in the lows, mids and highs, all of them. It is also at the cranked volume when the dynamic issues will stand out the most. You might for instance have a snare that has much too much high mids and highs for instance, quite common even among commercial mixes.
In my view it depends on how much it is turned down and how dynamic the quiet sound sources are. The quiet parts in a mix are the first to go below the perception threshold, beyond keeping the ears fresh mixing at low volume can ensure the quiet sound sources get enough signal in the mix.
I’m sorry, but this is patently false.
1. Mixes that sound good quiet typically hold up very well at loud volumes. Any exceptions to this are anecdotal at best, or mix engineer error at worst.
2. It’s a false assumption that you get “higher information density” (I’m interpreting that as meaning you get more information about what you are hearing into your brain). The reality is that the way the human ear works, when you go too loud (too loud being a combination of both volume, and time exposed – with the emphasis on volume), you actually get LESS information about the sound into the brain. There has been tones of research going back many many decades on this.
3. The threshold of hearing is technically 0dB at 1kHz. In practice, it’s more like 4dB. That’s REALLY freakin’ quiet.
Which brings me to two points to consider. If you consistently find that you need to listen LOUD (as loud as the OP is talking about) to get a balanced mix and to hear details in your mix, then one or both of the following is mostly likely the reason:
1) You are mixing in a noisy environment. If you have traffic noise, noisy A/C units, other noises in the house, noisy computer fan, etc. That will all mask sounds in your mix. The louder that stuff is, the louder you need to listen in order to compensate for that ‘noise floor’. I would suggest you make a thorough evaluation of your mixing environment. You don’t have to go hardcore like me and keep computers in another room and seal the damn place up to make it dead silent. But you should minimize background noise as much as is conveniently possible.
2) You have moderate to serious hearing loss. This is a common problem that causes people to mix loud, particularly folks that have been doing this for a long time and slowly have to keep cranking it up as they get older and build more damage. And of course, the more you do that, the more you exacerbate the hearing loss. The hearing damage causes, essentially, dips (or holes as one audiologist that tested me likes to call them, because it’s scarier and forces people to take stuff seriously) in the frequencies you can hear. So in order to get those frequencies loud enough to hear them adequately you have to turn everything up. You should periodically have hearing checked with an audiologist. I do it every few years. It’s also a good idea to never listen to loud music for long periods of time, and wear earplugs at concerts, whenever using the lawn mower, power tools, in any kind of noisy environment.
But seriously, I can almost promise with near 100% accuracy that unless you are monitoring loud just because you like the feeling of music hitting you in the chest, you have one of the two above problems.