By adding another perspective to the video, there's a whole different dynamic, which can lead to more entertaining streams and a better user experience.
As noted, Facebook does appear to be shifting focus in live, with an increased focus on new, exclusive TV-type programming, including the recent addition of Major League Baseball broadcasts.
Not only does it give users who might hesitate to use the video feature a little more confidence if they can have a friend with them, but it potentially adds more engagement to the mix.
The green eye indicates that those users are already watching the stream, while the others are not - you can now start a chat with non-viewers that will directly connect them to the stream, generating more exposure for Live content and enabling users to interact in a more personally relevant, intimate way.
Still, however, no integrations with Instagram’s other huge stablemate under the Facebook umbrella: Whats App.
The logic behind adding guests is clear for Instagram.
If there's too many low-quality streams, that lessens the viability of live-streaming overall, which could be another consideration in Facebook's shift towards TV-style live videos.
In line with this, Facebook has announced two new Facebook Live features which both lean more towards boosting the entertainment value of streaming by providing new capacity for exposure and discussion, and adding more perspective and engagement within a stream.