Actually the cache isn't that important, most binaries get rebuilt quite often due to their dependencies changing. Sure. But it's still nice that e.g. on Linux

Actually the cache isn't that important, most binaries get rebuilt quite often due to their dependencies changing. Sure. But it's still nice that e.g. on Linux x86_64 you can use a nixpkgs commit from 2015 and get all stuff from the binary cache.