I'm confused by this- there are two different questions here. what are you actually asking? what does "save it" mean? Do you mean battery life, or actual life of the monitor?
I'm going to guess you're trying to ask if it saves battery life, and the answer is "yes," but not nearly as much as if you, say, turned off wireless connectivity - airport sucks battery life way down.
It only turns off the backlight if you hold it. I figure its the next best thing to actually shutting off the screen, but I wish there was a way to shut off the screen as well.