LR has the wonderful feature of a virtual copy. Sometimes, while editing an image, I wonder which might result in the better photo. I can go back in the history and choose a point where I am still clear about my process, create a virtual copy and then continue with the differing ways of editing. I will have 2 images as an end result that I can easily compare and then make a decision which one I like better.
The same applies if I have different ideas about the final look of an image and so I can start out with virtual copies. It also opens up the possibility to edit one for the highlights and the other for the shadows. By selecting both, they can be exported into CS4 and combined there.
In a future entry, showing a before and after image, I plan on sharing a creative application of virtual copies to better represent the mood / weather.
As I see it, the big benefit of a virtual copy is the fact that it eats hardly any memory compared to a full blown duplication of an image.