As an editor, I've worked on books such as Kim Paffenroth's DYING TO LIVE and David Wong's JOHN DIES AT THE END. Track changes, an editing tool in Microsoft Word, has been indispensable.
With track changes activated, editors can strike through material for suggested deletions and can insert additions, which will be underlined and highlighted for visibility; reviewers can quickly cycle through and accept/reject the editorial changes.
I not only use this utility for editing; I also use it in my own work, to keep track of revisions and drafts. For example, Richard Finney and I used track changes while collaborating on our novel DEMON DAYS, to show each other the parts we changed.
To teach writers how to use the tool, I created a short video demonstration that I thought I'd share. The following instructions are based on Microsoft Word 2000. While tool bars appear differently in other versions of Word, the functions remain the same.