How Important to be Interactive?

Ellen says, in an interactive art work, "the andience is actually involoved in the artwork. tather than only exposed to the artwork". My question is : when the audience's reaction and the artist's creation involved at the same time, how important is the simultaniousness mean? Is there anything change in terms of "authenticity"? And, does the interaction have to be face to face?

I think another charming thing about digital media is, it can always allow the artist across the boundries, from photos to vidios, to films, we don't even know what is the next. It is not about the technology, it is about the concept, no matter it is interactive or not.