I'm not convinced that's the case for Friends. I'll again refer to the DVD special features, there's one where they show how the studio audience helps rewrite the final cut of the show.

The example given is, they're in Vegas, Chandler and Monica are thinking about getting married, to the point Monica is wearing a "borrowed" blue sweatshirt, when Ross and Rachel barge in, faces covered in marker, having just gotten spur of the moment drunk Vegas married.

In the script, Chandler's line is "I think they're drunk." This got a cool reaction from the audience; in this moment Monica would deliver a straight line and Chandler would quip off of it. So they did another take where Matthew Perry improvised the line "I think they're two bottles of vodka in human form." which got a larger audience reaction, and that's the take that was broadcast.