Nixos-rebuild - same build-host / target-host VS use-substitutes

Could you please explain is there a difference between these two commands?

nixos-rebuild boot --build-host myremotecomp --target-host myremotecomp --flake /x/y/z#myremotecomp
nixos-rebuild boot   --use-substitutes       --target-host myremotecomp --flake /x/y/z#myremotecomp

I understand why to use build / target host. But the nixos-rebuild doesn’t complain when I pass same build and target host - is that an alternative to --use-substitutes?

Thank you.