Why some anti-aircraft positions stayed empty in surface combat

Were light anti-aircraft batteries left unmanned during surface actions and crewed only under air attack?

Some were, especially mounts atop main turrets where blast made their positions unsafe during surface firing.

Dual-purpose batteries would normally remain crewed, but light 20 mm and 40 mm mounts placed on main turrets were a different matter. Those weapons were valuable under air attack, yet their exposed locations became dangerous when the main battery fired beneath them. Blast concussion and the disturbed airflow around outgoing heavy shells could injure or kill anyone remaining at the mounts. Their crews therefore shifted to damage-control parties or other duties during a surface action rather than standing idle. A weapon could be tactically available while its mounting remained unsafe to occupy in that kind of combat.