HDMI-CEC was supposed to make home theater setups a lot easier to work with. At first, it seems like the kind of feature that would just work, but then the problems arise. The annoying part is that the protocol isn't broken exactly. It just has issues when it comes to handling the way most people actually build their setups. So it's better to turn it off.
HDMI-CEC may have too many problems to be useful
Your devices are always talking over each other
HDMI-CEC (Consumer Electronics Control) was supposed to be the feature that made home theater setups effortless. The idea was that one remote would control everything. Press power on your Apple TV or PlayStation, and your TV turns on, your receiver wakes up, and everything switches to the right input automatically. It runs over a single wire on Pin 13 of your HDMI cable, letting all your devices talk to each other behind the scenes.
The problem is that it isn't as simple as it seems and tends to have trouble working cleanly. The HDMI spec lets manufacturers build their own proprietary commands on top of the base protocol, so instead of one universal system, you get Sony's Bravia Sync, Samsung's Anynet+, LG's Simplink, and so on. These branded versions tend to work fine when all your gear is from the same brand, but the moment you mix a Samsung TV with a Pioneer receiver and an Apple TV, things start…