(whistles you away from my potter fanfic...948k and nowhere near done...)
BW is trying to lead you down the path of better character building, less “smut-only” story, which is definitely one I try to pursue myself. Obviously, the shorter the story, the less of that character buildup will be in the actual prose, however, it’s useful for guiding how the character responds to situations, especially when it’s out-of-ordinary responses (ie, I had a grown man breakdown & cry when he saw my teenage MC naked because it reminded him of discovering his own son dead from carbon monoxide poisoning – same MC who loved oysters but had the allergic effect of giving him a bad case of the runs).
As to introducing those characters, I’ll typically give a distinguishing physical feature or two (ie. hair color) though sometimes it’ll simply be “the waiter” even if I know they’ve got magical birthmarks on their tosh. Having a warstory or three in their bio-sheet is good too, but don’t forget to actually write the story you intended to write!