I've found that shooting too much with a bent arm can result in injury. I'm going through physical therapy for tendonitis in my bow arm. It is a result of trying to shoot with the bent bow arm.

Like Paul posted, don't lock it either. That will probably hurt you faster than bent.

I think that the elbow should be balanced so that the forces are going through the joint with the least muscle involvment possible. This is how the Korean kids can shoot 1,000 arrows a day without injury.