On the phone with a friend in Cali this morning. He said that some municipalities are requiring /4 (12-3 or 14-3 romex) wiring for all new construction or rewiring for overhead lighting components. Maybe they love the use of fans or know that in the future that the extra wire could help with energy savings when using a central lighting system.
I have personally always used /4 for this because I am always afraid that someone will change their mind and want a fan (I install a fan brace too). I am wondering if there is any code to back up the wiring requirements in different parts of the US or world and what you would offer advice as best practice?