Every other sitcom forever. They had the good sense to film I Love Lucy in long, theatrical takes in front of a live audience, so the laughter you hear is essentially genuine. But not every performer is as badass as Lucille Ball to basically nail the first take every time. So in basically every sitcom since, they have to use canned laughter, even when it's filmed in front of a studio audience--a joke just isn't funny when you've seen it five times in a row. Let alone shows like MASH, where they filmed on location. (Words cannot describe my gratitude when I found that the DVDs gave me the option to turn the laugh track off.) Our generation has largely been spoiled by Scrubs, which eschewed a multiple camera set up and laugh track.