it probably depends on the warrior using the shield, and the type of battle. The Kite shield, as used at the Battle of Hastings, helped to protect the whole body. After the introduction of full body armour, knight's shields became smaller. The buckler, was a small shield carried at the waist and used in hand to hand fighting. The larger, round, target shield, was commonly carried by ordinary soldiers. Wall shields were used by archers, mainly crossbow men, to duck behind whilst reloading. English and Welsh long-bowmen had little use of them, it is said that at Agincourt, one arrow was striking home, the next was in the air and the third was being knocked, that's too quick for ducking behind a shield each time.