Subdivision surfaces differ from polygonal meshes in 3D modeling by their core structure and detail generation: polygonal meshes use fixed flat polygons (triangles, quads) to directly define shape with static vertices/edges, while subdivision surfaces start with a simple base mesh and apply iterative subdivision rules to generate smooth, high-resolution surfaces.
Polygonal meshes have a fixed polygon count, making their structure easy to edit but prone to faceting with low polygon numbers, as each polygon remains flat. Subdivision surfaces, by contrast, iteratively split edges/vertices to add detail, letting artists control shape via the base mesh while achieving natural smoothness.
For organic models (e.g., characters, curved objects), subdivision surfaces excel at smooth, lifelike results; for hard-surface models with sharp edges (e.g., machinery), polygonal meshes often offer more direct, precise editing control.