Factorio Forums

Why would it use spoilage if there is carbon fiber or bioflux?

It’s about the Game Design opportunity, not just “what makes sense”. Spoilage is initially seen as “waste to be thrown away”, then it becomes semi-useful as a burnable fuel. With the introduction of Biological ingredients for advanced products it becomes necessary to produce Quality Spoilage purposefully in order to scale these Modules; so Spoilage is now a full-fledged Ingredient!

Or you can pretend that Efficiency Module 3 works by Mushroom Magic.

Many players will have to "deal with their spoilage accumulating", it's part of the game. Offering a receipe that uses spoilage as ingredient is part of the tools available for the player to achieve this.

That's 1 reason i can see.