If you are using Facebook social apps for watching videos, reading content and you don't want your friends or everyone to know about your activity, you can turn this off.
If you put your computer into hibernation, the next time you turn it on, you'll get all your windows and programs open just the way they were before the shutdown.
If you want to put your video files online using HTML5 then it's recommended to have three different formats for a full browser support. Those formats are mp4, ogv and webm.
