For the Old Masters of the Renaissance and Baroque, drawing from the model was a means to an end—usually some sort of narrative or allegorical invention. One drew from the model to study form in light, particular anatomical issues, and foreshortening. This is why, from Raphael to Pietro da Cortona, life drawings rarely took more than an hour to complete. The artists had bigger fish to fry. I work within that same tradition, which instills a particular approach to delineation and rendering, whose principles you can find here.
The masters must be copied over and over again, and it is only after proving yourself a good copyist that you should reasonably be permitted to draw a radish from nature.