Two advantages to this method:
*I could do my last read-through at lunch and away from my computer.
*A good way to help you edit is to change the font/format/etc., which can trick your mind into thinking the document is new. Changing from a 13" laptop screen to a black-and-white Kindle screen...well, that's certainly a different way to look at the document!
The main disadvantage is that your changes aren't instantly reflected in the document. But that's also an advantage...I tend to make changes impulsively, and knowing that you have to do extra work to make a change helps keep you from changing something unless it needs changed. In the late stages of editing, that can be a good thing.