Its like in TV. The season builds to a finale, which is usually a cliffhanger, that connects into the following season's premire. & it works. Using Star trek as an example, I really couldnt care less if I missed an episode of TNG. So what? It didnt matter. & ultimatly after 7 years & two movies, all that happened was they blew up the D & got the E to fight the Borg. Same with early DS9 & Voyager.
Buffy always built to a final confrontation.
A comedy like 30Rock, Friends, or the American Office can just be a bunch of 100+ episodes. But a show about heros has to build to something.