We ran into this concept recently in a manuscript by one of my private editing clients, who was kind enough to consent to a discussion of the topic here on the blog. Though the client's work inspired the post, all examples are mine.
Here's the issue in a nutshell: When do we present actions undertaken by groups of people as aggregate actions, and when do we isolate individuals and track their actions as representative of the group?
Generally, we're going to be better off with the specific, unique example. In fact, that will be true of almost every case. But sometimes aggregating the characters can be a quick shorthand for setting a scene or accomplishing other tasks. The dividing line between these two choices -- the individual and the group -- isn't drawn in a permanent location, but it's almost always going to be better to stick to the individual.
This might be clearer if we consider an example. Your heroine is a 14-year-old girl, a freshman in high school, and the event is a gym class in which they're learning to dance. Class is assembling but has not yet been called to order. Our heroine -- let's call her Kendra -- is with a cluster of her girlfriends on one side of the gym. The boys are all milling awkwardly on the other side of the gym. There's one boy in particular Kendra would like to have as a partner, but at the moment, her more pressing concern is where she'll fall on the pecking order. She doesn't want to be the last girl picked, or even in the bottom half.
If we describe the entire event in the aggregate, we might have something like this:
The girls huddled together along one side of the gym and pretended not to watch the boys along the other wall. The boys were bolder. Their shoulders squared up to the girls in a forthright manner, though most of them also slouched enough to prevent direct eye contact. Feet shuffled. A shower of giggles erupted from one cluster of girls, followed by a squeal, a high-pitched protest, and more giggling. The boys seemed to take courage from this and bumped each other as they milled about in the casual manner of athletes in a huddle. Any moment now, they would begin pairing off.
So, let's start with this question: Which of these pieces of action is better off being isolated and attached to a single character, and which would you leave in the aggregate?