The parts in my designs are fairly simple and mathematical (rectangles with holes like Lego Technic), which makes them good candidates for OpenSCAD. My product

The parts in my designs are fairly simple and mathematical (rectangles with holes like Lego Technic), which makes them good candidates for OpenSCAD. My product designs, though, are first made by hand in a playing-with-Lego-like way (3D printing parts made in OpenSCAD as needed). Beyond that, I like having the precision of source code for my designs. Like source code, I can easily check them into source control and track changes over time.