Sketch workflow using Solidworks 2007:
Whats the point you ask. Why dont you just finish it up in CAD? Why take a screen grab and jump to another program? Well- for one detail geometry in a model takes exponentially longer to create. Overlay sketches get the ideas across quick and easy
Also , there is a psychological reason for doing so. You cannot imagine how quickly a CAD model can stifle discussion. As soon as you put some sketch lines onto a screen grab, you give your team tacit hints that you are looking for input. Conversely the closer to a photo your render looks, the more likely that you can convince a development team of a direction you feel strongly about.
This side view view is an overlay (blue and grey screen) done in Corel Painter, over simple geometry (white surfaces) in Solidworks 2007.
The screen can then be applied as a decal to the Solidworks model and tumbled around.