The evolution of the episode count: How many episodes is too many?

How many episodes should a season or series of television be? Of course, there will always be TV lovers who give shows like "X-Files," "Friends," "The Office," "Smallville," and "Supernatural" a chance despite being over 200 episodes long, or in "Supernatural's" case over 300, but the time of the long running series is drawing to a close outside of procedurals. Obviously, established shows or vehicles with big name actors can get away with feature length episodes of television, but that's still a lot of time for viewers to invest in a series. While there isn't a consensus on how many episodes is the sweet spot for streaming shows, it does seem that 8-10 episodes per season works well for shows. 13-15 episodes would likely produce tighter storytelling especially for series where there's clearly not enough material to stretch past that marker.