The idea of Yahoo Livetext is to make you feel closer to the person you're chatting with. Because it uses images and no sound, you'll be able to use this app anywhere. You can use this tool as a simple messenger, with the difference that you'll be able to see the other person's streaming image.
Keep in mind that you don't have to do anything for the other person to see you. Once you start responding to a message, you'll be able to see the other person. You won't have to activate your camera: it will turn on automatically once you start typing.
Yahoo Livetext is an instant messaging app that should be commended for trying to do something different. Many other apps just imitate the features of the most popular apps, and it's nice that Yahoo! is trying something new. Now, all that's left is to hope other users like to be see each other while they chat.