Some shows have managed to withstand the test of time without a laugh track, but laughter is social, and it's contagious, which is one of the reason why many shows began to use laugh tracks in the first place: it's easier for people to laugh at something when they're with other people, as opposed to by themselves, so in a sense, the purpose of laugh tracks is to recreate the atmosphere of actually being with other people (since before television, people would see movies or plays or things like that in theaters, in the presence of other people, where it was okay to laugh as loud and much as you wanted), and since in a number of cases, live audiences were either cost-prohibiting, or simply not practical (shows like TMS or ALF are such elaborated staged shows, audiences aren't going to want to sit through all the different cuts and camera angles, and set adjustments and such).