I think you just answered your own question with this.
When you're at the receiving end of an artillery barrage, you would
really be glad that you have a helmet.
In fact, if I remember correctly, the military helmet was invented
on the battlefields of WWI. In the past, they used to wear useless
cloth caps. If I'm not wrong, it was a French soldier who
ingeniously put a metal pot over his head to help him survive the
shrapnel of a German artillery bombardment.
In addition, even if it can't stop a direct hit by a 5.56mm round,
it can still deflect an indirect hit sometimes. If the round hits
the helmet at an angle instead of head-on, there's a chance that
the round will be deflected.
The effects are also psychological. I sure as heck would feel a lot
better to have a helmet on when the bullets are flying all around
me.
