Scales only the final canvas element on the page. The WebGL backbuffer stays at the logical game size, then the browser stretches that bitmap to the CSS display size. This preserves low-resolution/pixel-art rendering and does not add more fragments while scaling up.
Scales the canvas by increasing the WebGL backbuffer size. The logical game size stays the same, but rendering happens at the final display resolution, so rotated sprites, lines, and geometry get more rasterized pixels and look smoother.