Mouse movement for the most part is way more efficient then keyboard movement.
Sure, you need the keyboard to strafe, but that's about it.
You also need the keyboard to have the slaves move independently of the main.

You can mouse look, via the left button so much faster then you can via a keyboard.
You can mouse turn, via right click and moving the mouse a lot quicker then you can on the keyboard again.

The back key is pretty much useless. You can turn and strafe at double the speed.
Even if you want to break follow, a forward keypress does this as well as a back press, but forward is not a useless key.

If you're using WASD, either unbind AD or QE. The turn keys are not needed, but Strafe is still useful.
The S key is inferior to a turn and strafe for backwards motion, and just duplicates the W key for breaking follow.

If you shift your fingers to ESDF, its the same thing as WASD, except you have keybinds on either side of the movement keys.
You still only need, E (Forward) and S/F (Strafe Left/Right).

When researching keybinds, some players have really weird things.
I've seen R/F for forward/back and E/D for left/right, which seemed very awkward.
WASD is the most common, but ESDF is popular too.