Consider the following cases:
1) You want to hot-swap your keyboards and have the adjustment carry over between keyboards.
2) You want to switching between host terminals and virtual machines and have the adjustment carry over into the various VMs.
3) You want the adjustment to affect the BIOS as well.
4) Your keyboard is on a KVM switch and you want the change to affect multiple computers that may be running different OS's.
In the above cases, it would be handy to have a physical "bump in the cable" adapter.