Just like the rules, the fluff isn't entirely set in stone. You can use, not-use, rearrange, do what ever you want with it. It is just there to give you a feel and
inspire you (read: not take over). No matter how imaginative you are, you will always do better if you have some sort of outside influence - be it talking to another person, reading a novel, listening to music. And by "do better" I mean you will get more ideas than just going it alone in your own head.
This harkens back to another thread about Tool-box games vs. Integrated games. I was raised in the era of integrated games where you would have a complete game come out, both rules and setting. Like Psi-World, Gangbusters, Star Ace. In some cases, the rules would be minor-to-moderate adjustments of existing rules if the games were made by the same company. Fantasy Games Unlimited (FGU) was big on this; they would put out a game every 6 months or so, with a different setting/genre but the rules were modifications of the rules used for the earlier games (and, generally had a DnD/ADnD feel to them). I like this (though not the DnD like rules
).
I am ok with tool-box games* (Hero system is a prime example) but they do have a tendancy to be very complex with all the "stuff" there for any genre of game. It is too much. I pick up the Hero 5th edition and use it for weightlifting!! Oh, then they will put out a genre book that streamlines it down for you to cover just those things of a (insert genre here) nature. But that is ANOTHER book. Unless you want to spend the work-week full of hours to do it yourself, you need to buy the book.
That is book bloat.
*So long as someone is willing to put in the work on designing every little item, spell/power/psionic ability, race, plant, animal, magical creature, magical rock, psionic rock, technological rock....ok I am sure you get my point. I have fun playing the games much more than working on the behind the scenes stuff. Though I do have some fun doing that, just not the massively tedious rules/number-crunching stuff. I like coming up with the plots, NPCs personal aspects and drives, that sort of stuff.