Mostly speed, I'm mostly doing large boolean unions of primitives or chain hulls and OpenSCAD chugs pretty good at large numbers of operations. Don't get me wrong, they're great tools for what they're good at. I need to do more research before I start a port, SDFs seem like the best option but I'm not 100% confident. I am considering using your SDF library though (github.com/fogleman/sdf) but need do do some experimenting/benchmarking first.
Not sure if this matters for you or not, but my understanding (with some experiments) is that the "slicers" implicitly do a union. As in: you could have an STL with a bunch of overlapping blobs and the 3d printer slicing code just checks isInside -- which is effectively a union.
At least that's what I found when I was generating STLs in code.
