Most MCUs can mutate their flash, though, and most large embedded projects have one or two weird features that depend on mutating flash and then accessing it as

Most MCUs can mutate their flash, though, and most large embedded projects have one or two weird features that depend on mutating flash and then accessing it as const data. Also, Harvard architectures like AVR have different address spaces for flash vs. ram, so const variables still end up copied into RAM unless you qualify the variable types with non-standard decorators. Being able to explicitly tell the compiler, "you can and should compile this out" seems like a good thing?