Quote Originally Posted by Bootsiuv
I'm fairly certain there most common role was to ferry fresh troops from the camp, and take the wounded out. They were rarely involved in actual melee.
That's ox-carts. We're talking war chariots here - expensive, prestigious, specialised war machines requiring considerable expertise and infrastructure to field.

The Celts used theirs to move elite warriors around. The chariot made a decently fast and maneuverable platform from which to throw javelins at the enemy ranks and generally impress the snot out of them, and allowed the senior warriors to deploy into combat swiftly and get out of a tight spot if need be. And should the enemy ranks start looking suitably thin, ragged and wavering a chariot charge made for a good final straw to break the proverbial camel's back.

...the Bronze Age Middle Eastern ones would really require a whole new topic by themselves, and aren't relevant anyway.