What Gives a Show Rewatch Value?

Some shows and movies are rerun over and over again on popular TV networks (like ABC Family's Harry Potter Weekend that is repeated a few times per year and AMC's "The Walking Dead" marathons), while others are hardly ever replayed. Networks seem to choose shows that viewers want to see multiple times. What gives certain shows and movies rewatch value? What qualities do they have that makes viewers want to see them numerous times?