Shield beyond sight, ne'er failing light--
Palings are mainly used to protect cities from air-strike. Certain enemies are also capable of erecting small-scale palings to protect themselves. Palings protecting cities appear to be held up by magic from powerful crystals or magicite, by a group of chanting priests.
During the battle of Nalbina Fortress, Prince Rasler and Basch fon Ronsenburg fight to defend the fortress against the Imperial forces. The Empire's aerial fleet is unable to attack the town as the paling protects the fortress, but the infantry has managed to penetrate the city's defenses.
As the soldiers enter the tower where the crystal holding up the paling is located, and slaughter the priests, the paling is broken and the imperial airships are able to attack the town. The paling's fall marked the fortress's defeat.
During the battle above Rabanastre, the Sky Fortress Bahamut fires the Mist cannon from the Cannon Superstructure, which hits the Resistance Carrier Galuf-Val and two other ships. As the Mist concentration explodes, it spread across the Rabanastre airspace. The city's blue paling repel the shockwave as well as the airship debris.
The city suffers more damage when several other airships crashed into the paling; while it managed to reduce the debris into blue mist, smaller debris manage to penetrate the shield. When the Bahamut is in danger of falling on the city, which would break the paling, Judge Zargabaath comments that should Rabanastre's paling fall, the city would be destroyed. Unlike in Nalbina, the paling's mechanism was not shown.
The miners around Bhujerba mention that since the paling that kept the mines' monsters at bay has fallen, they have been unable to continue work. It can be speculated that Marquis Ondore has let the paling fall on purpose to hinder the Empire's flow of magicite.
In Final Fantasy XIII, Palings serve as roadblocks to certain areas within the world of Gran Pulse. Accepting and completing certain missions from Cie'th Stones will remove these Palings, allowing the player to explore new areas and accept further missions.
Palings are created across the cities of Valendia to protect them from the reaches of The Dark. It is revealed by Jan Rosencrantz that the Valendian Parliament is responsible for this act, as part of their plan to control the Dark, taking it over from the Bardorba bloodline.
By creating these palings, the Dark has no choice but to focus on Leá Monde's population. After the fall of Leá Monde, a paling was created across the city to keep the Dark monsters within. However, Sydney Losstarot and his Müllenkamp cultists are flooding the city with more monsters, it is feared that the paling would fall.