OpenGL vs. OpenCL, which to choose and why?

Question

What features make OpenCL unique to choose over OpenGL with GLSL for calculations? Despite the graphic related terminology and inpractical datatypes, is there any real caveat to

Answer 1

OpenCL (in 2.0 version) describes heterogeneous computational environment, where every component of system can both produce & consume tasks, generated by other system components. No more CPU, GPU (etc) notions are longer needed - you have just Host & Device(s).

OpenGL, in opposite, has strict division to CPU, which is task producer & GPU, which is task consumer. That's not bad, as less flexibility ensures greater performance. OpenGL is just more narrow-scope instrument.