Nothing, in first century Britain said you had made it as a warrior more clearly than having your own chariot.  Celtic warfare was a ritualized affair of heroic one on one combat, peer against peer.  There was no honour in fighting someone of lower ability or class so individuals would make it clear who they intended to fight before the battle began.  For the Celt warfare was a cultural expression, for the Roman it was a day at the office.

The Celtic hero was accompanied by a servant whose job it was to do all the unmanly, heroic things.  These include driving the chariot, holding the warriors cloak whilst he fought, holding the spare weapons and making the lunch.  He could be identified by a yellow circle on his forehead and was more of a piece of the warriors kit than a servant or slave.  For a graphic illustration of this relationship consider Ukko from the Slaine series in 2oooAD.

The chariot was essential but it was more heroic to be driven than to drive.  The hero would stand with his, or her, hair was blown by the wind whilst the servant took him to his next fight.  He would dismount and the chariot withdraw to a safe distance ready to sweep him up once he had won.  This was not a piece of kit for fighting but a battlefield transport enabling him to sweep in on his enemies, to get him from A to B in style, and then at the end of the day allows him to sweep home with a brace of heads to decorate his home.