This could be great for people on old hardware, because it reduces installation times drastically.
But old computers also benefit the most from custom, highly optimized compilation, so I don't really see the point of this move.
I see it as just another option. There are some packages that are annoying to compile (and don't yield much performance gain from doing so) that can now just be pulled from the binary cache. The old way was to have specific -bin packages, but that is a bit arbitrary and presumably this is a bit more scalable.