High poly counts make 3D models heavy because each polygon adds data that increases file size and requires more processing power to render. More polygons mean more vertices, edges, and face information to store—straining memory for loading/storing the model—and more work for GPUs/CPUs, which is critical for real-time uses like sprites where smooth performance matters. To lighten the load, try decimation (reducing polys while keeping key details) or LOD systems (showing fewer polys when the model is distant)—both preserve quality without the extra heaviness.
