me and my friends used to spend hours doing line for line copies of comic book drawings when we were 10-12 years old, its a natural part of the process i think...

Dunno. I strongly believe it really depends. I never did that, for exactly the reasons other people lay out in this thread, "but what if I want to draw something else?" (actually "but I want to draw something else, this drawing already exists anyway, why copy it").

Some of my friends did like to copy drawings. A lot of them never progressed past that, and some did. It really depends.