The main idea behind reading your work backwards is that it takes the anticipation out of it. When you've written something and reviewed it numerous times, your brain actually reaches a point of auto-pilot. You're not really reading what is in front of you, but instead anticipating what comes next.
It's no different than having watched the same movie over and over again. You reach the point you can recite dialogue or mimic the character's movements. You may not even need to watch the screen if there is background music or noise to give your brain a cue because it is working from memory.
I was taught this technique in college, and it was reinforced at my first newspaper job. Of course, this was before the advent of spellcheck and each word had to be reviewed. But it is still a useful technique if, like others have said, you do it one sentence at a time. Even if you have a word processor with spell/grammar check, some systems may not catch usage mistakes similar to "there", "their" or "they're". By looking at each individual sentence, you'll find these errors.
Keep in mind, it doesn't matter where you start. Go one scene at a time and work backwards or start at the end of the chapter. It doesn't mean you have to start at the back of the book and work all the way to the beginning.