I was tempted to use that once, but whatever I had at the time had no input blocking option.
Now I won't use it unless really pissed off ever since I've let our L2 to remote into my machine so they could remote into a machine they couldn't reach for some reason. They decided for some reason block my input, at which moment I was startled by this thing stretched over the full screen. Not even the guy who was remoting in was aware of that.
I wonder if it is possible to customize what's shown onscreen on those, we expected the lock screen to be just blank/black until that moment.