The Fan has been in every Super Smash Bros. game to date. It has weak attacks, but they are very rapid and can add up damage. Also, it can be a KOing projectile when thrown if the foe is at a high percentage, since it has good knockback when thrown.
In Super Smash Bros. Melee, it is generally considered the second best item with which to diminish an opponent's shield (a fully charged smash attack with the fan will break any shield).