The purpose of the design sketch is: first, the communication between designers and products; The second is the communication between designers and people. The former has nothing to do with hand-painted techniques. The most important thing at this stage is divergence and storm. Of course, this is based on full perception of all dimensions of the product. The latter requires designers to use 2D methods to let others understand your creativity. Of course, the better the look, the more intuitive the better. (Personal Humble Opinion)