YouTube offers privacy options for sharing live streaming through Google+ Circles. This can be beneficial if for example your company has an all employee, all hands or town hall style live webcast and you want to limit the stream to only your employees. Or if you want to offer a live stream of a conference, seminar or live concert - but only to a specific audience - such as those who have purchased the event. Then you can add the audience into your G+ Circle and they will get an invitation email to view the stream.
This method is a way to increase the private event outside of the previous 50 person limit. Each viewer however must have a Google+ account.
This is a very powerful and easy option for secure live streaming on YT. It also leads to some powerful viewer metrics.
Here is the YouTube support link that explains Private and Unlisted Videos on YouTube.
The important paragraph in this support selection is:
- If you use your Google+ identity on YouTube, you do not have a 50 person limit on sharing, as private video sharing is done to Google+ circles. There is no limit to the number of circles to which a Google+ user can share.
- In order to watch a private video, your contacts must already have a YouTube account. If they don't already have an account, they'll first need to sign up for an account. If they do not sign into their account before watching the video, the video will not load.