Stuff seems to be funnier in person. Like, if you're a fan of the show and you're in the audience and you're excited, you'll laugh at the drop of a hat. It's also, like, we're used to seeing people be funny on TV, but when the person is right in front of you, any funniness seems more like a novelty. (Hope that doesn't sound like bull, I don't really know a better way to say it..) I've even seen the phenomenon get made fun of briefly on other shows. (Like in the episode of South Park with the fake TV psychics.)
But yeah, I bet they also add laughter or cue it on a screen for some shows.
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"You gotta keep making decisions, even if they're wrong decisions, you know. If you don't make decisions, you're stuffed."
- Joe Simpson