The concept is that one shot situates the subject in its environment, the second is the entirety of the subject in isolation, and the third is a detail of the subject. For example, I have a courthouse series in which I photograph courthouses around the world. One photo is usually of the courthouse that shows its location, either in the center of a city block or on a square, with the courthouse itself not filling the entire frame. The focus is on the entire building in the second. The third shot may be of just the doors or one of the symbols of justice that may be on the dome.
The method is not limited to architecture. A landscape may show a broad area, particularly with a wide angle lens, then a more defined portion that is still broad enough to show the vista, and finally, a tree or rock may be isolated. Street photography works the same; a broad shot of the entire street in context, a more focused image of several storefronts, and finally, a particular window, door or sign. By having the three images, we capture the overall impression, a study of the subject, and a detail that sheds light on the personality.
As an example:
It’s just something to think about as you approach a subject and makes for a good exercise in training yourself to see the many different opportunities.