Comment Logging is taking an extra precaution when users edit their comments. If you have a long timer or unlimited editing enabled, logging will store all edits of a comment.
The edited comment is stored on the individual comment in the admin, and you can easily revert back to the original comment.
With Comment Logging and Stats enabled, when a user leaves a comment, it is stored for reference so you can keep track of edits for a particular comment.
You can check out the edits for the comment, and even restore a previous edit.
Here's a quick demo of reverting a comment.