[z303]

Guessing here but so they can be turned into a polygon model for easier display, yes you can directly volume render the data but say a 1024 x 1024 x 1024 cube even at a byte per voxel would be a large amount of memory, most of which will be empty

I'm guessing OpenCL is being used to accelerate Marching cubes or some other similar algorithm

http://en.wikipedia.org/wiki/Marching_cubes

This post by Smash of Fairlight http://directtovideo.wordpress.com/2011/05/03/numb-res/ talks about some of the reason why you want to do this but in a very different context