The biggest benefit of using 3d CAD to design and prototype my work is the number of intermediate fabrication steps it bypasses. Once a design is settled upon, the digital version of the sculpture is basically finished; there may be a few loose ends and problems to address, but at this point the only thing left to do is to generate 2D CAD files to drive the cutting of the material. No maquette or other physical prototype is necessary, saving time and wasted material. Care does need to be taken to insure that the simpleton fabricator (me) can assemble the parts once they're cut; careful labeling and color-coding are a huge help.
2D "Crop" for the laser cutter ^.
The "Crop" model, with parts in context.