Early television had a problem -- it was really new and weird. People were used to radio shows, but those required you to imagine everything that happened, not watch it happen for you. People were also used to plays, but those were seen in the company of many others, an event to leave the house for, not to slump on the couch and mindlessly watch.
People just really didn't know what to do with television, so t.v. producers quickly realized they were largely going to have to tell people what to do. And one of the most direct ways this was accomplished was in telling you when to laugh, by supplying an audience to laugh for you. In many ways, this recreated the theater experience, in which there were a lot of cues about when it was ok to laugh, right in your home, in which there usually weren't too many other folks around to supply such social cues. It says something powerful about the social effects of the behavior of our peers, but that's yet another post.
Nowadays laugh tracks are sneered at by the television intelligentsia, who have moved on to their fancy single-cam shows filled with snarky references to current events. But this being America, there are a lot of people scared by such developments who prefer the comfort of a pre-recorded audience telling them when to laugh.
The people turn to places like CBS, where everything is designed to primarily appeal to people over 75. But to not completely denigrate these laugh-track shows, they do require a certain talent. Much like the theater, the actors have to learn to allow for pauses as anything they might say would be overpowered by the audience's laughter (although in the theater, it's actual human beings laughing). As such, they really do need to develop a certain kind of comedic timing. A type of timing that is completely creepy without the canned laughter filling the spaces.
Take for example this clip of the Big Bang Theory (which, all told, is really not that bad a show), presented with only the laugh track missing (embedding for some reason disabled). It's eerily compelling...