Unlimited Shot is a Ranger job ability in Final Fantasy XI. It allows the Ranger to fire a shot without using up arrows or ammunition. The ability is gained at level 51 and can be used once every 3 minutes.
While this may not seem incredibly useful, it is used mostly to macro-swap out normal arrows for one, sometimes unique, high damage arrow to perform a devastating Weapon Skill.
The following macro, which may not be the best or safest way to do the macro, shows an example of what a player might do to perform a weapon skill somewhere in their 50s. After gaining the TP they need to perform a weapon skill, they would use this macro to switch out their normal, Darksteel bolts with a Gold Musketeer's Bolt. Darksteel bolts are DMG 50, while the Gold Musketeer's Bolt is DMG 60 and offers +10 Ranged Attack and +20 Ranged Accuracy bonus. Even without knowing the precise mechanics, the Musketeer's bolt is clearly a superior ammunition. In fact, the bolt costs 32,000+ Conquest Points for just one.
After switching the ammunition, the Ranger activates unlimited shot. The wait command gives them 3 seconds to cancel the macro if they are unable to activate the job ability (/ja is the command for job ability), and then they use their Weapon skill, Sidewinder (/ws is short for Weapon skill). Performing the Weapon skill takes a second or two usually. The final line will switch the Ranger back to using normal arrows.
/equip Ammo "Gold Musketeer's Bolt" /ja "Unlimited Shot" <me> /wait 3 /ws "Sidewinder" <t> /wait 3 /equip Ammo "Darksteel Bolt"