So I've been considering this for a while, even before this thread came up. Believe it or not, my thinking was actually triggered by Lady Gaga's video for "Applause." It struck me as odd that a video about applauding does not show a single shot of an audience. This led to some thought about the difference between passive & active consumption, particularly in American entertainment.
Television is the most passive of media forms. There is no interaction expected from the audience, and the viewers have grown accustomed to accepting the standard television format of content/commercial alternation. However, theatre mandates a live audience. The audience at a live performance has a very critical role, both in terms of their response and their silence as a group. The responses of an audience inform the rest of those present on proper/improper reactions to the events portrayed.
This also led me to consider the importance of the audience in more restrictive states. Back in the communist era of the USSR, theatre productions would run as "dress rehearsals" for months on end and never actually open. Opening would subject them to review by the government censors, but as long as the shows were running as "rehearsals" they were able to get their message out to as many people as possible. It seems very "first world" to me that American culture has grown so disconnected from the crucial presence of the audience, when other cultures have had to go to such lengths - and recently at that - to make sure it survives.
Attending a big rock concert or a sporting event will not have the same effect as attending a live theatre performance with a smaller group. Live theatre teaches the audience that even their silence has an effect - a lesson that I think is absolutely mandatory and sadly missing in the modern American consumer/viewer.