i think you shouldn't bend your bow arm. i don't think you should lock it either. it should be as relaxed as you can get it, and straight. bending it makes you use your muscles which is not good imho. to see which is stronger go lean against a tree with a bent arm and see how long you can do it compared to having your arm straight. the less muscle involvement the better and more repeatable you form can be. but, in the end its whatever works better for you.