Scale is a tool used by artists that allows for them to visually shape a scene and add to the context simply by using size and perspective. In the manga adaptation of the webcomic, One Punch Man, scale is utilized many times throughout the series to showcase the main character’s strength. In the scene pictured, a giant monster’s face has smashed through his apartment. The monster is held back by Saitama, who is only half the size of the monster’s mouth and is doing so one-handed. When examining this scene, the reader understands how strong Saitama is, even without being told directly, and the scale allows for a direct comparison due the difference in size and the simplicity of the exchange between them.
Another example of scale is shown below the scene between Saitama and the monster. Saitama’s friend King is shown huddling in the back in fear. When Saitama speaks to him, most of his upper body is in the panel along with a speech bubble below his face. When King thinks to himself, his face is shown much more closely to “the camera” and is drawn in more detail in order to showcase his much more terrified expression.
In short, I would say the greatest effects of scale are context and emphasis. Scale is the “flavoring” of a scene that can make action scenes more dynamic and impressive and dramatic scenes more emotional.