When it comes to perspective anyway! When designing a realistic painting, artists should keep in mind that the size and scale of objects within a composition are important. Objects that are closer to you generally appear larger in size than objects in the distance. Things diminish in size as they recede into the picture plane. The rock formations in the painting depicted here are a good example. The scale should make sense if you wish to show depth. For example, you would not want to paint chairs which appear larger than figures, or fruit that seems larger than a bottle of wine. A mistake of this kind will decrease visual depth because the picture will look less plausible.
Due to the demands of perspective, you may, however, have a chair that is actually drawn larger than a figure if that chair is in the foreground and the figure is in the background. The key is to use perspective to make different-sized elements appear to make sense within the picture plane. Always examine your paintings with a critical eye, looking for anything that does not visually make sense. If one arm or leg on a figure looks longer than the other, does it appear correct because of the perspective (or foreshortening) in which it is drawn or does it appear to be an error?
When realism is not the goal, scale can be intentionally exaggerated to give a piece a more stylized feel. This can be a great tool for the artist provided he can make certain it seems deliberate, rather than just incorrect. If the artist is working on a more abstract or non-representational piece where perspective and scale are irrelevant, the size of shapes used in a composition can aid in establishing a sense of visual depth. Any shape that is different in size from all other shapes can become an immediate focal point.
Size does matter.