If you like updates and sharing, Twitch’s latest update to Friends ought to make you happy.
“You can now share what you are watching or broadcasting with your entire friends list. Not only that, but you can easily join them by clicking their status under their username. Now your friends list will not only show you who’s online, but also show you what everyone is up to at a glance and even hop into a stream with them!”
If you’d rather keep your stream watching activity private, there’s a very easy way to disable it.