Because of what sounded like a conflict between what Rick Welch was teaching and what it appeared Rod Jenkins was endorsing in another thread, I asked Rod about the difference. His view was the arm should be fully extended, but that you should not go the extra step of engaging muscle to lock the elbow.
Rod's view and Rick's differ, if at all, by a matter of a very few degrees of elbow bend. So, in my opinion McDave is right - stay with what works for you because the difference among the experts doesn't amount to much.
On the issue of shoulder damage, I'd be willing to bet a substantial amount that far more shoulder problems are caused by being over-bowed than by elbow angle. I'd also be willing to be that if you are over-bowed, a locked elbow will do more shoulder damage than a bent elbow, just because there's no place other than the shoulder for the force to go.