As I understand it, it's best used in bombers. Padlock will train all gun positions on the target that can see it. Those guns will fire when you fire. So if you're manning the tail turret and have a target padlocked that's coming in high from the left, the top turret and left waist guns will also track and fire on the target as you engage from the tail. As he dives through low to the right and you shift to ball turret, the right waist gun will track and fire on the target as you engage from the ball turret. Padlock increases your fire power especially when in formation, because the same drone gun positions will track and fire along with you. The other guns are only as accurate as your aim though from whatever gun position you are manning.