Actually, it's less complicated than that. Steeping is letting the
juice sit for awhile.
Taking the lid off would be letting it breathe and given that nicotine oxidizes with contact with air, letting it breathe would be good for
juice that needs more bitter in the taste.
How do you know if it needs steeping? Taste it. If it doesn't work for you then let it steep. If it still does not work for you, then it didn't need it and you could PIF it or swap it on the Classified. If it works for you after steeping, then it needed it.
I mix my own. Some of my mixes need steeping. Many don't. I know from experience which is which.
I would think only
juice that is made to order would ever need steeping.