This tool takes each particle from your original simulation and replaces it with 10 new ones. This will give you more sand without having to simulate more sand. It will essentially create a bunch of particles around the existing particle, and will maintain the same motion as the original particle. The simulation will be exactly the same (no new motion) but is very useful wet sand situations to add extra texture.
Using Upres Sand
Select the geometry object to convert to RBD grains.
Click the Upres Sand tool on the Grains tab.
The following shows the before and after rendered images of a squab rising up from being buried under the sand.
You can control how many particles are generated using the Points per Point parameter on the Point Replicate DOP. The default is 10 particles for each original particle.
For specific parameter information, see the Point Replicate help.