I have tried this but cannot get a consistent wake up - when the cover is opened again I can see the backlit keys but the screen is black - hitting the power key just puts it back into sleep again ! What do you do to wake it up ?
I was reminded of this particular problem today when my SP4 apparently would not wake from sleep. Your device may actually be waking from sleep except that the lock screen is located OFF OF THE SCREEN, as in, it is way up such that you cannot see it nor is it activatable. I have had this happen mostly when I use it like a tablet, put it to sleep, connect the keyboard, and then wake it up before it goes into hibernate. One of a few tricks to get past this black screen is to hit ctrl+alt+delete which will take you to your login screen.