In archery, it is important to keep your shoulders in line. In picture A, the individual would have a difficult time aiming because they are using their muscles to hold the bow. I realize that you use muscles to hold the bow, but in picture B, the individual is using the bones in their arm to hold the pressure of the bow, allowing for a steadier aim.
Correct hand position in archery is a vital part of your form. An incorrect grip can cause torque on the bow causing the arrow to fling left and right. Keep a 45 degree angle grip as well as a relaxed hand to limit your impact on the shot.