I can imagine a scenario where the bandwidth is so slow, and the client CPU is so fast, that theoretically sending a small file that is expanded into CSS would

I can imagine a scenario where the bandwidth is so slow, and the client CPU is so fast, that theoretically sending a small file that is expanded into CSS would result in a faster page load. The use of JS Web Workers might further this. In addition, with more mobile internet providers capping monthly usage, every byte counts. I'm assuming that these CSS compilers generate larger output CSS files than their input.