This is not pointless because there are so many ways to play Minecraft. He/she is building the most efficient way to create Cacti. It's almost like playing a bean counting or resource management game. On top of it, he/she built a beautiful temple around it. It's brilliant and one of the great possibilities of playing Minecraft.
Couldn't have put it better myself.
There needs to be a better use for Cacti than occasionally hurting mobs now. Do it for this guy and this guy only!