What effect does adjusting the size parameter of a particle in Unity have?

Adjusting the size parameter of a particle in Unity directly modifies how the particle is visually represented on the screen. By changing the size, you can make the particle appear larger or smaller, which affects how it interacts with the game's environment and can influence the player's perception, adding to the overall visual impact of the particle effect. This is crucial for designing effects like smoke, fire, or sparkles, where the visual scale can dramatically change the effect's clarity and presence.

Other parameters, such as weight, duration, and color, serve separate functions in particle systems. Adjusting weight generally relates to physics properties, duration affects how long the particle exists before disappearing, and color would manipulate the hue and saturation, none of which directly correspond to the size parameter. Thus, the fundamental purpose of changing size is to enhance visual representation, confirming that option C is correct.