Frederick Copleston, A History of Philosophy, Volume I: Greece and Rome (Westminster: Newman, 1959) 365.
Aristotle demands...unity of plot, in the sense of organic, structural unity. The plot must be neither so vast that it cannot be taken in at once by the memory nor so short that it is small and insignificant. But he points out that unity of plot "does not consist, as some suppose, in its having one man as its subject," nor in describing everything that happens to the hero. The ideal is that the several incidents of the plot should be so connected "that the transposal or withdrawal of any one of them will disjoin and dislocate the whole. For that which makes no perceptible difference by its presence or absence is no real part of the whole."
There are plenty of television episodes, movies, and books that can be summarized according to a simple plot. Star Wars is about a hero who sets out to save a princess and ends up destroying the enemy's powerful weapon. You take out one of the main characters, and things don't run as smoothly.
Then there are stories in which the characters may not actually meet, yet they are connected in some way: through a relationship, or something that's happening to all of them. I think of the movie Magnolia. Crash is supposedly like this as well.
Some stories can have a clear plot-line, yet the author feels free to go on tangents. Dostoevsky's The Brothers Karamazov comes to mind. The story is about a man accused of murdering his father, yet it gets into profound discussions about religion, atheism, nihilism, etc., etc.
There are stories in which we have more than one plot. Middlemarch is like that. Soap operas such as Dallas can be like that as well: we see what's going on with Pam and J.R. and Sue Ellen and Miss Ellie, according to their own individual lives. The plots usually don't have much to do with one another.
Then there are times when all the plots comment on a common theme. The second season of 7th Heaven was like this. In the episode "I Hate You," all of the sub-plots were about hate. The same goes with the episode "Red Tape." Does real life work this neatly? Not necessarily, but I still liked the order on these particular episodes.
I like stories that have order: a clear point, a solid beginning, middle, and end, etc. But I also like some stories in which there isn't much order, in which I can simply hang around with the characters and empathize with their experiences.
But there are exceptions, such as when there are too many characters and plot-lines for me to keep track of. I don't like that so much, since part of my enjoyment of a story is for me to get to know the characters. So some depth is needed, and that may hinder breadth.