Close-ups, medium shots, and full shots not only have a purpose individually, but as a whole. For example, a full shot can establish the location of a dialogue shot, then the director can "cut away" to a medium shot to identify the recipient and avoid an awkward cut. A formal "cut-away" shot cuts away from the action at hand to something else. For example, the boy in the cityscape meets up with his Mafia friends. They have a dialogue, and during that dialogue, an eyewitness looking out a nearby window sees the conversation. The director can cut away to the eyewitness both to introduce a new element in the story and enable the dialogue shot to change in some way, such as camera angle. Transitioning from a full shot to another full shot is uncomfortable for the viewer, and it breaks the shot flow. The cut-away shot allows the director to transition between similar shots, such as a full shot to a full shot, by cutting to a different type of shot, such as a medium shot, in between. A cut-away shot can be used to merge similar shots together or to hide mistakes. Figures 6 and 7 show two shots: one a is dialogue, and the other is a cut-away from the eyewitness point of view. Here, the cut-away shot helps break the monotony of the dialogue shot while enabling the viewer to gain a sense of to whom the character is speaking.
Figure 6 A dialogue shot between two characters. It's a lengthy conversation, so a cut-away shot can help break up the monotony.
Figure 7 A cut-away shot breaks up the dialogue, and it also introduces the viewer to a secret eyewitness peering from a building window.
Cut-always are just one way for a director to change a shot. While close-ups, medium shots, and full shots are generally used with a static camera, you can animate the camera for a different look.