Refactoring is something you are doing all of the time whether you realize it or not. It is an essential part of coding, and helps to reduce defects (Kim et al.). Sometimes, you may find yourself saying "this method would make much more sense if it was named..." and now you're plodding around changing every usage of that method to the new name. What a waste of time; you might as well have left the name nonsensical!
Refactoring tools help you accomplish this by automatically changing the usages for you. Plus, refactoring tools help you avoid mistakes in refactoring. Pretty soon, computers will be programming themselves!
Kim, Miryung, Thomas Zimmermann, and Nachiappan Nagappan. "A field study of refactoring challenges and benefits." http://www.msr-waypoint.net/pubs/172573/kim-fse-2012.pdf