well, a common application is 3D noise. One can easily make a 3D noise volume texture of say, 64*64*64 and sample it using tex3D(3dsampler,position.xyz). Because you are sampling a 3D texture it is consistent across space and time.

3D noise is useful for things like volumetric fog, fractal terrain, planets, etc.

Currently I'm working a planet renderer in A8 using 3D noise to procedurally generate terrain on a sphere.