This is mainly a self-challenge piece--making both products without having any byproducts to deal with. Feed in Crude Oil, Sulphur, and Titanium Crystals and you get both Casimir Crystals and Plastic for your late-game needs (Plane Filters and Particle Broadband) without having to worry about excess hydrogen or graphite.
It's also a showcase of the various belt-fu techniques I've been learning as of late, featuring a super-slim assembler array and some very tighty-packed chemical plants.