Vehicles have always been an integral part of the Halo universe and matchmaking in particular. For large scale games, it is sometimes infeasible to run across the map rather than driving. Because of this and the unique qualities of each vehicle in halo, they have become a much beloved function of the game, serving important purposes while still being unique enough to personify certain styles of play (or even by a playstyle in their own right).
Note that while only UNSC and Covenant Vehicles have been revealed, it has not been ruled out that the Prometheans don't have some sort of vehicular transportation.
