If you read/watch a review for certain big budget films these days, you will most likely find the reviewer criticizing the length of said film. Many modern blockbusters feature a runtime between two and a half hours, and three hours. To many people, sitting down to watch a movie than long can be a difficult task, but as long as the filmmakers know what they're doing they can make a long movie that audiences are willing to watch. However, it's quite obvious when a movie runs too long due to certain aspects that run through most overly long movies.
One of the best examples of proper and improper use of length in film can both be found in the "Middle-Earth" series of films. The "Lord of the Rings" trilogy is a good example of long movies, each film averages out to about 2 hours 50 minutes (unless were talking about the extended editions that average out to about 3 hours 30 minutes each). Despite the massive length of each film audiences fell in love with these films. These films have a lot of locations, characters, and side plots; but the films never lose focus on the main quest to destroy the one ring and make Middle Earth a better place. Almost everything that happens in these films is in service to that main quest. It also helps that the characters are defined, dimensional, and a lot of fun to be around.
On the other hand, a bad example of length in film is the "Hobbit" trilogy. While I wouldn't go as far as to call them terrible movies, their length (which is equivalent to the "Lord of the Rings" trilogy) is a massive issue. It's extremely clear that, because they were adapting a much shorter book this time, they didn't have enough material to justify the length. To fill those holes, they add additional material from other Tolkien works and original scenes that are meant to connect them to the "Lord of the Rings" trilogy. However, this causes the film to lose focus and the main plot often gets derailed in favor of setting up things that happen in future films that are unrelated to the film at hand. Also the third "Hobbit" film almost has no real plot, it's basically a two and a half hour battle conclusion. Things like this are usually used for the third act of one movie, not stretched over an entire film.
There are more examples of films using their lengths in good and bad ways, but I think you got the gist of it. Films often feel overly long when they don't put enough material in them to justify the length. They feel like they're stretching out scenes that should be simple and quick in order to "run out the clock". Films like these could benefit from another pass by the editors to tighten up the story's pacing and keep the narrative focused. Hopefully people can take the same lesson from this article as the one from the "Lord of the Rings" films: "What matters is what you do with the time that is given to you".
