There’s a fantastic blog somewhere out there (I failed to find it, Google skills clearly lacking) that illustrates why we don’t just resize our assets, but have each icon set redrawn by a designer, if big images looked good when scaled down we just automate the scaling process or use SVG – but they don’t! Icons need intelligent redesign at lower-res, the designer adapts a layout when using less pixels, eg. a keyboard might be redrawn to have less keys, a bigger asset might display full qwertyuiop, a lo-res version just qwerty. The qwertyuiop asset scaled down would be a blurry fuzzy mess.