If you have a large-ish project that is otherwise coded in Rust, but you have to do some low-level coding because of special I/O, or special intrinsic features

If you have a large-ish project that is otherwise coded in Rust, but you have to do some low-level coding because of special I/O, or special intrinsic features for multimedia, or even just flat-out performance, then this allows you to do so without falling back on linking against ASM or C.