actually, summaries can enhance the reader's understanding.
for example, if i were to summarize the great gatsby, i would make sure to note the theme of time that reoccurs through the novel. "jumping over sundials", "in the meantime, in between time", the chapter that is merely a timeline of events during the summer, gatsby knocking over the clock when he sees daisy again (and others i'm sure i've missed).
i would also point out that nick carroway has a gay encounter in the elevator while drunk at the end of one chapter. most people would miss that, especially if you're a righty douche like the copy and pasters here.