From The 07K Wiki
What is Virtual Dyno ?
Allows to use different kind of logs format in order to generate a dyno graph based of your car's acceleration. While properly configured, it gives accurate results as a real dynamometer would (Ex: DynoJet, Mustang Dyno for example). It's possible to log AFR ratio and absolute manifold pressure to see its correlation to the graph.
Who should use it ?
Anyone can use VirtualDyno, especially those who doesn't have access to a physical one. It helps to keep track on ignition timing gains as you can see how the changes affect the engine's output. It can give an overview of the engine's performance.