Does --no-substitutes save bandwidth?

[Luther]

I've installed Guix 0.2 on my Ubuntu system. As I type this, I'm using
it to install gcc. If all goes well, I hope to soon install Trisquel as
my base system with Guix as a package manager.

I'm trying to save as much bandwidth as possible, so I started the
daemon with --no-substitutes. But it occurred to me that binaries might
not be much bigger than source tarballs, even with documentation. What
do you guys think? Would --no-substitutes be generally useful for saving
bandwidth?

Luther