Sometimes I can edit my works-in-progress on the computer. But, honestly, my best editing happens on the printed-off page with a pen in my hand. Why?
I can be messy. Sometimes editing on a screen is too clean. I need to be able to manually circle, underline, and scribble. This is also when I can be the most blunt with myself and ask "What were you thinking?"
I can measure word count. Feeling the heft of a manuscript--regardless if it is too short or too long--creates a sense of accomplishment, especially for the rough draft. Simply filling the paper tray of the printer can provide the illusion of completion. There is much more to do. But, at least something has been done.
I can manipulate the pages. It is highly possible--even with an outline--that parts of the story are misplaced. A hard copy makes it possible to read from beginning to ending and find out where the story needs to be shifted. Or maybe there is part of the story missing all together. Now is the time to see the gaps and add to the outline.
Of course, the next task is to enter in the edits. But, the beauty of that is reading through the manuscript again and making more decisions. On with the process!