Change of pixel dimension
When you want to change from resolution 800480 to 1024600 there is a slight differeence in pixel dimension to remain circle shaped objects. So idea is that you are able to change pixel dimension and convert some files, instead of drawing new ones. For example-you have a circled object in some .ai file, where you have square pixels. If AI would allow to change pixel shape to rectangular, like 0,14mm height and 0,15mm width, or 0,148mm,..., than it would fasten up things of making same graphic for different screen resolution with tool of pixel dimensions, instead of drawing whole new screen.