The specific use case is limited.  You can created an realtime interactive topo by moving sand around within a sandbox. However, if you extend this technology, this is where it gets interesting.  Say for example, you place two beams next to each other, then ‘fuse’ those beams in AR.  You can now do stress tests in real time.  Take a bit of clay, shape a car and see the resulting aerodynamics as you work on it.  Perhaps you are laying out a new freeway interchange, you can see the traffic simulation adjust in realtime.  There is already a form of this with various game controllers using video tracking and converting that to inputs for the system.

Check out the project going on at UCDavis called the Augmented Reality Sandbox project.

..and check out the Video below.