Often in life, it is the nice little touches that make you smile and please the most.
If I have my 1520 in a cradle in my car and am on a long trip... The power button is difficult to reach due to the cradle's grip. For the device to be secure it must obscure the power button.
I will certainly use this feature to put the screen to sleep on long stretches when the nav is not needed, but runs in the background and combined with double tap to wake now provides me with a more elegant and well rounded solution to a minor irritant.
Bravo.