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Well, in my case, I found it useful for Macro photography.
When you are shooting at distances bellow 10 cm, focus could be hard. If you can see right away the final image, you can make small changes...

Yap, i use DSLRdashboard, similar to that one, works very well with my Nikon D70
I did a video to my magazine:

http://youtu.be/U2Xk2_I_5PM