It allows a web developer to choose the quality/performance tradeoff when scaling images. There are 3 options in total: low, medium and high.
Docs: https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/imageSmoothingQuality
Samples: https://jsfiddle.net/khru0mzj/ https://drive.google.com/a/google.com/file/d/0BySFHAS13VhbRVBUM3dHaDV3VFU/view