NicoVideo audience can add overlay comments on the video and people can enjoy or discuss anything realtime. Many Otaku people like to watch the live streaming of NicoVideo and put many comments. Sometimes they insert the geek words and critical comments. This is not happen on the broadcasting because it's filtered by TV stuffs but NicoVideo provides no filtering video contents.
Audience can watch the movie by free, but when many people watch the video such as premium concert, the amount of audience is limited like a real concert hall.
If people pay 500yen($6) per month, they are treated as premium users like an airline service. People can keep premium sheet and are not ousted.