I don't really understand the argument for constraining a drawing. Maybe it is just the jargon I don't understand. If you make a 3D drawing to the specs you want produced, that should be it. It was it when I did in with a paper and drawing pencil. Maybe what you are saying is that you should provide to a shop not only a 3D STEP file, sheet or otherwise, but to have a dimensioned drawing along with it. Like a PDF. However, with a Model or Sheet Metal, you can use Measure to check your dimensions without the dimensioned PDF. Where does the word or concept of Constrained come in to this? If I draw a 4" x 4" box, that should be considered constrained.