Originally posted by BrianR Mirror Lock-up takes care of vibrations caused by mirror slap, but doesn't help with the moving mechanical shutter.
Extremely high magnification macro people will also benefit.
You're right, they are different things, I wasn't really paying attention.
The other day I was playing with my kp, and found that in live view with the electronic shutter and the aperture preset or wide open, manual focus, shake reduction off, and a few other things, its totally silent and inert.
Not much use to me, but for scientific applications it's probably extremely useful.