As Part of a Larger Paper
Summaries of various sorts fit into larger papers. We often see summaries as part of a review of literature that sets the context for the writer's research or position in a controversy. Sometimes writers use summaries of polarized arguments to show the range of points of view in a dispute. Even more often, summaries are frequently used as "proof" for an argument or your position, to explain a given idea or fact, or to show where the information you are using came from. This is why many writers compose summaries frequently as they are researching for a larger essay. Writing a complete summary of each essay/book you cover in your research is a good time-saver because you can simply "paste" the summary at an appropriate point in your draft or refer to it for a central quote or idea.
When you're using summaries for one of these purposes, be sure to think about what your readers already know about the topic. If your readers know relatively little on your topic, your summaries will almost certainly be longer and give readers more background information. If you believe that your readers know a good deal about your topic, you can probably set the context or prove your point with a précis or brief summary.