It could be a weapon that you move quicker and jump higher with so it basically increases your general agility when held. There could be different effects with each type of arrow, and you press X to change arrow types instead of reload. For example, there could be poison arrows or paralysis arrows that stop the enemy in place for a few seconds. Berserk arrows could turn the enemy on their allies (obviously wouldn't work on bosses though :P). Perhaps there could be recovery arrows that heal your fireteam members when shot at them. It's really more of a support weapon type than anything.