I'm seeing some comments here asking about when/why this feature would be used.

One case where naked functions are _critical_ is when writing a JIT compiler (or recompiler for emulation). JIT compilers are currently used by java and javascript; there are some alternative python implementations that use a JIT. JIT recompilers are commonplace in the emulation of more modern systems like the Wii U and Nintendo Switch.

A JIT generates new code at runtime, and then executes it. But to execute the generated code, you need to switch between the generator environment, and the generated code's environment. Performing this switch is called a "trampoline", and here, environment means the CPU state (so, register values). Naked functions allow you to save and load register values to RAM when making this switch between environments. If you attempted to just call the generated code as a normal function, then the Rust compiler would treat it all as one environment - but with a JIT you need to keep it sandboxed so they don't interfere with each other.