When I download a drawing like my latest tree work, I get some of this, and it's a good question and one that needs to be thought through by every realist. Why not just take a photo, or why bother with all this work when it’s already documented?
That's a great question and a realist has to answer this for him or herself, If copying without change, construction and re-invention, be it form a photograph or from life, then the creative process is not addressed, in this case I agree there is a useless element about it, it becomes a fundamental exercise at best. There is nothing wrong with these exercises if it improves your knowledge and