I turned on the comments section of this video for a little back and forth on the definition of steeping. I had to turn it off and will probably turn it off again because it is troll bait. By all means read the comments...
How To Steep Fresh Juice for the Best Flavor - YouTube
PG is mainly used due it's thinner properties and the fact that it mimics throat hit. All custom juice makers will suggest steeping their juices which will involve removing the cap, exposing it to air, and letting it sit for short period of time before use.
Chinese juice makers like DeKang and others employ "warming" to expedite the steeping process at time of manufacturing. As for a "dark cool place" it really means a place of moderate room temperature and not exposed to UV ie sunlight. I place mine in a closet during this process mostly because it is out of the way and not as exposed to dust. Nicotine is UV sensitive and has no reaction in color or otherwise to fluorescent or incandescent lighting.
To learn more about steeping simply google "Steeping E-Juice"
I don't agree with many of terms used in vaping nomenclature, but I have accepted the fact that a butt plug as related to vaping is a battery connector insert and not an adult toy.