Portability

Carrying people around on your back is endemic in anime so it's no surprise that Ashitaka ends up giving a ride to a casualty.

A little sign of Studio Ghibli's attention to detail: any other animation company would have made Ashitaka's bow disappear until it was needed again, at which point it would have magically reappeared.
 

Added: 4/24/10 From: Celga
 
Portability