I saw this yesterday and tried it out and it's pretty cool. No "lag" for me or the other person watching the stream. Although I noticed there's a delay of about 15 seconds from my computer to theirs. Not a big deal. This beta is looking good to me. It's really cool to be able to do this and I'm planning on letting anybody watch my games If they want. It is kind of creepy I guess though lol
https://steamcommunity.com/updates/broadcasting
https://steamcommunity.com/updates/broadcasting