4. The Creators Are Also The Cast & The Writers
A lot of the time, having your writers and your cast cross over a little bit can give a show a lot of room for improvisation and last minute improvements. In the case of It's Always Sunny, the creators of the show (Rob McElhenney and Glenn Howerton) star as Mac and Dennis. Charlie, another lead member of the gang, has also written a number of episodes... even David Hornsby (Rickety Cricket) has written a bunch of episodes! Behind the scenes stuff like that adds so much to a show - it kind of makes it into one big machine that just churns out comedy. These guys are talented and they know exactly what to do with their characters to make the show great.