Because it all depends on the culture, I just do what other people do. In things like Kabuki, it is a tradition to clap (or even shout out the actor's father in greater compliment) when a performer does a picturesque pose (mie) or changes costumes on stage. On national tours that I see, most people are indeed subscribers who sees shows often, and only gives standing ovations when appropriate. On Broadway, it's a totally different crowd.
And I don't blame just the tourists. I don't think EVERY tourists have the courage to be the initiator of those standing ovation. In most cases, those who initiate an entrance clap for the 8th replacement of Elphaba on the 2nd national tour are in fact a group of rabid Wicked fans who know every current, past, and future Elphaba/Glindas in every productions around the world. Even though it might not have been a standing-worthy performance, I'm guessing people would still give standing ovations to Angela Lansbury who hypothetically just gave the worst performance of her life in the crappiest show ever, simply because she is a Broadway legend. Many pretentious college MTs also go out of the usual to give thunderous ovation or even worship something that is currently "hip" to be obsessed over, like
Next to Normal. Then, there are a group of "elite" theater fans who complain and bitch about the ubiquitous occurence of standing O's who think they are the sole qualified group of individuals who determines what was a standing-worthy performance or not.
I don't initiate any standing ovations or clapping (unless at end of the song, show, etc), and I'll just do whatever what the general consensus in that theater decides to do.
"Hey, you! You're the worst thing to happen to musical theatre since Andrew Lloyd Webber!"
-Family Guy