A common question I get is what the difference between Lightroom’s Snapshots and Virtual Copies. While you could use them interchangeably in some ways, they really have two separate uses. Here goes:
What’s a Snapshot?
Think of a snapshot as something you’d use when editing a photo and you have a few different paths, editing ideas, or effects you want to try on the photo. It’d be silly to keep hitting the reset button and start over again each time. And if you found a good point where you liked how the photo looked, but wanted to try something difference just in case, you’d run the risk of forgetting what the settings where if you tried to revert back to it. Well, that’s where a Snapshot comes in handy. Basically, you’d get to a point where you like the photo and create a Snapshot in the Snapshots panel in the Develop module.

Lightroom creates a “Snapshot” of all of the current settings you have for that image at that exact point in time. Then you can go down another editing path. If you decide you like Path B, better than Path A, then you can leave things as they are. But if you decide you’d like to revert back to Path A, then you just go to the Snapshots panel and click the one you created for it. Lightroom reverts all of the settings to whatever you had when you created it. It’s essentially a tool to help with experimentation.
A popular follow up question to this is why not just go to the History panel and click on the History state where you liked the image best. I guess you could do it, but then you’d have to remember exactly what history state you liked which could be a pain.
Okay, Then What’s a Virtual Copy?
A Virtual Copy is Lightroom’s way to create versions. Let’s say you want to edit a photo and have a color version, a black and white version, and maybe a black and white with a slight color tint to it(done in the Split Toning panel). You could use Snapshots but you’d have to click from one, to the other each time you wanted to see the different “versions” of the photo. Most likely, when you have versions, you want to compare them next to each other or show some one else the different versions so they can pick their favorite. That’s where Virtual Copies help out a lot. You just right-click on the photo and choose Create Virtual Copy. Lightroom makes a copy of the photo. If you look in the filmstrip, you’ll know the virtual copy from the others because it has a little page curl icon on it.

At this point, go ahead and change the settings to the black and white. Then right-click again and create another virtual copy and add the tint you want to the photo. Now you have 3 virtual copies or “versions” of your photo so you can compare them next to each other and pick your favorite. What’s really nice is that virtual copies are, well, virtual. They don’t take up extra space and it’s not a real duplicate copy of the photo. But you can experiment as much as you’d like and you can even save JPEGs or print from the Virtual Copies.
I hope this helps clear up a few things. I know it’s a common question I get on my Lightroom seminars so hopefully it helps clear up some confusion. Have a great day!