If you're a 300 pound NFL lineman, size definitely matters. If you're a digital image file, it's a LOT more subtle! The true measure is pixel dimension. A one gigabyte file sent to Facebook will be resized to a file only 600 pixels on the long side because that's the size used in that application. That same one gigabyte file could be way too small for printing to a billboard, even thought the picture looks the same.