So what am I talking about? Well, it's the ability to be able to focus on the detail in your mix that you won't necessarily notice if you listen to it in your studio. This happens for a couple of reasons. Firstly it's that if you are changing your environment it will change your mindset, and change how you feel about the track. If you listen in headphones you can get inside a different headspace cut off from external auditory stimuli. Secondly, it forces you to listen to the track without being able to immediately adjust any of the parameters in the mix, as presumably you'll be listening on your phone or in your car or the like. This forces you to really listen critically and you'll often get an urge to change something when you're next at your DAW refining your mix. Thirdly, you aren't taking in visual stimulus from your DAW, meaning you aren't watching your mix but rather listening to it. The visual cortex in the brain takes up a large part of our brains processing power, and by breaking the link with your visual cortex you can analyse the mix or song purely through your auditory cortex, allowing you to hear things you haven't heard before.
Finally, if you choose to play your mix to a friend or audience, you'll immediately notice what needs to be changed with the mix or track structure without your audience saying anything, you'll become acutely self-conscious or aware of anything getting too boring or elements not having enough impact etc. Especially if your audience are also music producers.
Hope you found this useful. Stay tuned for a track coming from myself very shortly, click the video below for a preview: