Supporting Windows is often a pain (although in this case Rust hides a lot of that pain, honestly), but the main driver of the original sccache implementation was not Windows support, but the ability to share the compilation cache across our many ephemeral build machines. My colleague Mike Hommey (who wrote the first implemenation) has some nice graphs demonstrating this in his original blog posts on the topic: https://glandium.org/blog/?p=3079