If it adds to the story, you can probably keep it. If it distracts from the story, though, either drop it or rework it so it adds something. For example, if I wanted to add a new character, what does he do to the story? Let's say after reading story, I realize my MC comes off as a loner who can't make friends. That wasn't my intent, so I add a new character as a best friend who just pops up in the story every once in a while. I could even have the new character do something that helps the MC reach his goals (or stands in the way.) That makes more sense than just adding a character who has funny one liners, but doesn't do anything.
Fluff=something to fill the space. A filler. No writer would fill their story with irreverent twaddle. It would bore the reader. Perhaps you are talking about sub-plots, which are sometimes called fillers? Theses are used for pacing, taking the reader away from the action for a little while and giving them something else to consider but they are always reverent to the main plot.
You're whole interpretation hinges on the idea that the OP is using this as the definition of fluff. She's pulling this from a quote that I've heard before and agree with if you don't take the writer's terminology for the word fluff into consideration.
assuming you meant 'irrelevant' [since 'irreverent' makes no sense in this context] i'm sorry to say that is far from true... many, if not most of the aspiring/beginning writers i deal with as a mentor and writing services provider do exactly that! many of the excerpts i see posted on writing sites are fluff-filled, as well...
And do you help these aspiring writers de-fluff their work? Is there a lesson you can share that will help future poster keep their work from being invaded by this fluff?
yes, helping new writers to de-fluff their work is a major part of my mentoring... and no, i don't have any fixed lessons, but work with each mentee one-on-one, in whatever way works best for each, as there are too many variables... what works for one may not for another...