If you want to experiment with different versions of develop work on a photo, virtual copies and/or snapshots are two great ways to do this — all without having to create a second file on your hard drive. Snapshots allow you to save your work at different points in time so that you can easily get back to any point, and allow you to go off in different directions with a photo. Virtual copies in effect are separate copies of your photos, that can be developed differently. Watch the video below, from my Lightroom 5: The Fundamentals & Beyond workshop on video, to learn how to use virtual copies and snapshots. These techniques are applicable to later versions of Lightroom as well.
(For best quality, hit Play, then click on the Youtube sprocket wheel in the bottom right and choose 720/HD).