Of course, the other tasks are also crucial, so the question is - which ones can you afford to let NPCs take? Overall command/strategy, organizing the evacuation, leading raids and spoiling attacks against the enemy, running the large-scale defenses (your only shot at doing serious damage to many of the enemies), or defense of the troops on the fortification, whose wands can be useful for repair, reinforcement of shields, concentrated fire or otherwise.
As usual, I am online for discussion.