And you are going to want to embrace the ability to mute the volume considering that not only are uploaded videos playing automatically on the screen, but so are advertisements. Hey, Facebook needs to monetize, you know.
Look, we're willing to let you in on a little back door secret. Facebook would just feel awful if it forced you to use your precious data to watch a video, or even worse, an advertisement. So you can actually disable the auto play video on a cellular network so that it will work only when you're connected to a Wi-Fi pipeline.
While the auto play feature is only on the iOS version of Facebook, it is expected to come to other platforms as well.
Facebook for iOS allows you to disable auto play on cellular networks
source: Facebook via TUAW, SlashGear